This actually started last year, basically when you have extra weight in back of boat a small steady leak
of water comes thru the general area where trim hoses come thru transom assembly.
I had drive out over winter and could not see where it was coming thru ,
there was no water in drive bellows,shift bellows is only 2 years old,etc
Reasealed everything with fresh mercruiser gaskets but6 problem didnt go away.
The deeper the rear gets (such as launching or sitting on swim platform)
the worse it gets . It was suggested to me that it could be thru the steering arm as well.
Looking for ideas.

there is a seal on the steering pivot pin that can degrade and leak. If you can get your head in there with a light or even a small mirror and light, you should be able to see iif the water is coming in there.

There is also a small seal where the trim ram hoses terminate inb a coupling block which is bolted to the bottom of the transom assembly from outside.

I would check the steering arm seal like suggested. You should be able to see if it is leaking from inside with a flashlight. Had to change that one on my 2550. While you are in there put a wrench on the transom plate studs and make sure they are all tight.

I take it I would have to pull everything out to replace that?

If the boat is at home and on a trailer take your garden hose and have some one trace the out side of the transom area and the hole back of the boat at all the fittings and have some one on the inside with a light looking and lisening for running water. Make sure the inside is dry befor you start testing. Also test a round the rub rail for water leak. That is real commen. This should help pin point it.

Thanks, it is currently out of water as I try to get it ready for first poker run of year so Ill try your idea!
After having it apart for a long time I would dread having to pull engine again.
my boat is tall as heck for a 21 so rubrail is far away from water when this happens even with a couple people sitting on back..
You can see what I mean in attached pic , swim platform is about 10" out of water at rest . I have already checked all thru fittings and bolts/screws/brackets under/on/near waterline.

YEP

There is a gasket sealing the trim hose junction piece. Also if it had a merccathode or a zinc mounted there you should check and see if the plug is still in place

I had a link around the steering pin. It only linked when I was beached or had a lot of weight in the back. I found it by going to the ramp on a slow day and had somene back me in very slow until it started leaking.

It took a flashlight and a telescoping mirror to find.

exhaust bullhorns