On my 1997 MkII opening ports I was getting leaks I couldn't stop. I got the McMaster O-rings and cleaned the port gaskets but still had problems at the same rate. After talking with a C380 owner who solved a similar problem, I dug out the gasket that fills the gap between the outside aluminum trim ring halves. The gap is a little over 1/16" and runs horizontally at the 3 and 9 o'clock positions. The existing gasket was the consistency of plumbers putty. I dug it out with a razor knife and filled it with silicone. I had a couple good rains while on the boat last week. The opening ports are dry. I think these are the Lewmar ports.
Next stop, chain plates...
I had the same problem last year. Did the O rings and replaced the gasket. I think those are intended as expansion joints. I filled mine with silicone as well. Problem solved.
Mark Mueller