Legal Question in Real Estate Law in Michigan

You are correct, the time limit in Michigan for the "true owner" to file an action against the adverse possessor is 15 years. Your case is one of "Acquiescence", because all of the prior owners recognized and accepted the fence line as the "true" lot line for more than 15 years.

New Owner is barred by the statute of limitation.

The new owner should have ordered a survey before he closed the deal, and so if he didn't like the location, he didn't have to go through with the deal. He is stuck with the fence and the lot line now.

You don't have to do anything, unless he files suit to quiet title to that 30' in his name. At that point you will need to show that both parties, all through the chain of title going back for at least 15 years or more, farmed up to the fence, cut trees, cleared rocks, drove tractors, built structures, or whatever they did, up to the fence line, showing that each party possessed and used the land up to the fence line as if it was their land, and the land on the other side, belonged to the other.

Photos, records, testimony of any persons still living now who can sign an affidavit to this effect would help you, in the event that "new owner' wants to cause you problems.

You will likely need a real estate attorney to defend your position against him. You may also need to quiet title in your own name at some point if you decide to sell the property, and the lot line issue crops up again.