Couple of suggestions. First, try not to run the vent 100% open. They tend to hang up in that position more frequently. Second, lube the piston with white lithium grease and exercise it several times. I used that process on my 1994 370 and it was still working fine when I sold it in 2018.
I had a similar problem years ago. I found that lubricating the gasket with plumber's grease (silicone, not petroleum) cured my problem. It allowed the gasket to move with the deck and hatch lid when flexing.
I had a 1994 370 EC with the overboard discharge option. The seacock and thru-hull were located behind the port engine, almost against the hull side. The holding tank and waste pump were forward of the fuel tank, and the seacock and thru hull in the bottom of the boat were aft of the fuel tank.
I've been a member of a local yacht club for almost 20 years. You would probably call it a "blue-collar" club since we have no staff, members volunteer for various jobs, we have club work days and the clubhouse remains un-airconditioned for nostalgic purposes. We have lots of professionals as...
The PO of my 370 EC had one installed by some folks here in New Bern that work for Hatteras Yachts. Nice job. In our hot summers, it really is of little use unless in a covered slip (mine was). If away from my dock, it was useful at night, with the full enclosure zipped up. I probably got the...
I've sold my boat now, but it had a Sturdy sync. I loved it. One time, I had a problem with it and it turned out to be the sensor wire was not making good contact.
Oh, and I always engaged it around 1,000 rpm's. The momentary adjustment was less noticeable at the speed.