What follows is my own opinion, and should not reflect on MARA. This question is at core of another organization, Maine ROADWays, which is an acronym for Residents & Owners on Abandoned & Discontinued Ways. I'm afraid you have touched a raw nerve here - so if you want to skip over the details about the problems with the law and look only at possible solutions, scroll down to the last 3-4 paragraphs.
Are you looking to determine what is the right thing to do, or are you looking to identify loopholes in the law that allow the Town to escape any responsibility? To put it briefly, whoever shares the right to use a road should share the cost of maintenance so as to keep the road passable for their own use, as well as for the use of those who share that right. To do otherwise is to steal the value of maintenance from those who do provide it.
That is a huge flaw in the new law you mention. I was there when the law was being discussed by the Judiciary Committee of the Legislature, and I pointed out to them that as originally worded, only residential properties would share the cost of maintenance. If there were any wood lots, gravel pits, or commercial properties of any kind, they would get a free ride, even though use by heavy trucks could take a much greater toll on the road than residential use.
In response, the Judiciary Committee changed the first line to say, "...each property owner who shares the common benefit is responsible for a share of the cost of reasonable and necessary repairs to and maintenance of that private road..." Unfortunately, they failed to change the rest of the wording to correspond to the first line. In the Enforcement section, it says only that an owner of residential property can sue another owner of residential property who fails to pay their share. So although the law says that every property owner is responsible for sharing the cost of maintenance, there is no way under this law to force an owner of non-residential property to pay their share.
Under 23 MRS sections 3101-3104, if there are at least four property owners, any three of them can call a meeting to form a road association. But if there are not three who will agree to do that, then there is little that can be done. I am not at all surprised that the residents are reluctant to take on the cost of maintaining the road not only for their own use but for use by the public as well, when the public won't share the cost. Besides, members of the public who use the road do not have as great an interest in treading lightly on it, since their daily access to their home does not depend on it. They probably are not even aware of the damage that results from their use of the road. Residents must deal with it daily.
If there are three landowners who agree to call a meeting to form a road association, then every owner of property benefited by the road must be included in the notice of the meeting. That includes the town. If at the initial meeting the property owners agree to form that association, their powers include the ability to file a Notice of Claim (lien) against any property owner who fails to pay. But so far I have not heard of any road association that has ever succeeded in getting a town to pay dues to a road association where the town owns public land and the public uses the road to access that land.
The snag in all of this is that the Maine Supreme Court issued an "Opinion of the Justices" in which they said that use of public funds for the private purpose of maintaining a private road is unconstitutional. So towns generally use that as grounds for refusal to contribute anything towards maintenance of a private road. But if the public is a landowner on that road and uses the road for public access to that land, isn't maintenance of that access a public purpose?
Then there is the issue of the Constitutionality of public use of a road that is not maintained by the public. In 1968, the Legislature passed a law that was repealed just a few years later. 23 MRS 2068, the "Limited User Highway" law, allowed the Selectmen of a town to determine that a road was of limited use and value to the traveling public. Upon that determination, the town was no longer responsible for maintenance , but the road remained a public road. In 1970 in the case of Jordan v Canton, the Maine Supreme Court declared the law unconstitutional , and it was repealed soon afterwards.
In the Jordan case, the Court said that, "a public road with no public maintenance will inevitably be destroyed." Access is a property right attached to the land, and when that access is taken or damaged, the Constitution requires just compensation. The decision went on to say that it is the practical and factual consequences of governmental action rather than the legal status of the highway that determines Constitutionality. In other words, if the government does something that will inevitably destroy property access, and does not compensate the landowners, it doesn't matter whether the road is labelled a limited user highway, a private way, or any other designation. The uncompensated destruction of access is unconstitutional.
As I said at the outset, "Whoever shares the right to use a road should share the cost of maintenance so as to keep the road passable for their own use, as well as for the use of those who share that right." That is the right thing - and the Constitutional thing - to do. And that is why Maine ROADWays has been fighting for 40 years to try to get the laws changed. I think that if someone were to file a civil suit against a town for failure to share in the cost of maintenance of a private road that is used for access to public land, the Court would have a hard time absolving the town of responsibility.
There are a couple of possible options for addressing the issue under current law. First, 23 MRS 3105-A allows a town to vote to authorize the Selectmen to use public equipment on "private ways" when they deem it in the best interest of the public for fire and police protection. The term "private ways" as used in that series of statutes refers to "public easements," (see 23 MRS 3101) and many road associations have dedicated their roads to the public so as to allow the town to provide snow removal. The tradeoff is that the road is then open to public use.
Your situation raises an interesting question. Does the use of a private road for access to a public boat landing create a public easement over the road? If not, could the private owners of the road simply post or gate the road to prevent public use? Probably not, because the town as a landowner would have to be issued the key. But as a landowner, it seems the town would also be responsible for sharing in the maintenance costs.
The second possibility is 23 MRS 3106, which allows a town to grant money to repair a private road if doing so will protect or restore a Great Pond that has been identified by the DOT as "at risk." So then the question is whether the lake in question here fulfills the requirements listed under section 3106.