There have been discussios about installing an AirSep closed crankcase filter system on the Lehman on the Grand Banks owners forum. At least one person has done it. I recall the consensus of many of the members was that it was cost and effort with little return on investment.
The main issue, as I recall, is what to do about the oil breather overflow pipe. on the stock FL120, which we have, the breather pipe simply goes down into the air cleaner "cage" and the fumes are drawn back into the engine. How much actual oil ends up in the cage seems to vary from engine to engine. Ours put very little oil into the cage so the foam filter elements stay fairly dry and oil-free. We clean them perhaps every couple of years or so. I've heard of other FL120 that send a fair amount of oil down the pipe and into the cage and onto the foam filter element.
I recall that the conversion to the AirSep filter required dealing with the oil issue but I don't recall what was done. The AirSep website includes several Lehman models in their "Search by Engine" window but the illustrations don't change from model to model in the naturally aspirated models. So you'd probably have to call Walker Engineering and talk to someone.
The Smiths at American Diesel may know of alternatives to the stock filter setup, too.
