2005 Mercruiser V6 4.3L -water leaking into the engine

I tried to start the motor but it would not start and it wouldn't crank.
When I checked, water was mixed in with the engine oil.
I opened the cylinder head and found that only one side had water and the head gasket was intact.
So, I sent both cylinder heads to the machine shop for pressure test.
The result was no crack in both the head. So they resurfaced the cylinder head and
I assembled it back onto the engine.
I went for a test drive and the engine would be fine for about 30 mins on full speed
but after that, the water leaked into the engine again.
I re-opened the cylinder head and rechecked for any cracks by doing another pressure test.
The result came back the same with no cracks.
On a hunch , I changed the intake manifold. Nothing had changed and the same thing happened with
water leaking into the engine.
FYInly the left side of the engine is filling with watter.
Any ideas or suggestion would be greatly appreciated.

Ayuh,.... Ya already posted this question in the Merc forum, so why post it twice,..??

This just leads to confusion for those tryin' to help ya,.....

yeah sorry about that. it was my first time posting and I didn't know it would duplicate.