Solid Alarm Port Engine 98' 330 Sundancer 7.4 Mercs

[gater61]

Gauges all read okay, boat running great... BUT, if I cruise closer to 25 mph eventually port engine alarm will go on and remain on. (I tested to make sure it wasn't a bad sensor but when I pushed through the alarm I eventually noticed 'slipping'.) I got down and immediately checked trans fluid on both sides to compare. Port trans was very low on fluid when hot (almost nothing on stick), starboard side was fine. If I let things cool off for 45 min or so, I can start with no alarm and get back to cruising closer to 20 mph without issue. When I check trans fluid when all is cooled off both dipsticks show I have enough fluid... I just bought boat last month and had a survey and sea trail done, was told port trans was replaced in 2016.

Any "thoughts/ideas" would be appreciated. I'm not going to be able to repair myself most likely but would like to have better ideas when speaking to mechanic. Thanks all.