coolant loss on Peninsular "the Beast"

[Dujazz4]

Out last weekend in our 1994 28TE and after sitting at anchor for a while at the swimming hole and then getting underway, the high temp alarm went off. Found no visible coolant in reservoir over the heat exchanger. Added 1.5 gals and after running for 45 minutes back to mooring, checked coolant level again. OK when engine was warm, but no coolant visible next morning. It took another 2/3 gallon of coolant.

There isn't sign of coolant in the oil. There isn't evidence of coolant in the hot water system (no leak there). There is also no evidence of leaking into the bilge or the smell of coolant in the engine compartment (doesn't seem like a hose leak). A friend thought that he saw coolant coming out of exhaust when the engine was just started.
Had a local mechanic pressure test the fresh water side of the system and he believes that gaskets in the exhaust manifold are leaking and need replacement. I was hoping that this might be just a heat exchanger leak. The mechanic is questioning whether it makes sense to spend the money on replacing the gaskets (likely need to have made special, due to lack of availability from Peninsular and they would want to pull the engine). There are probably <1000 hours on this engine and the long block was replaced by Peninsular in 2013, however he's suggesting we repower.

I'd appreciate any thoughts...
Are leaking exhaust manifold gaskets the only likely problem, given the above? Any other testing that I could do to confirm?
Would you repower vs. try to fix? Suggestion on best option for repower....
Know of any good Peninsular mechanics in the northeast/Maine?

[Pedro]

I’ve following,,Any new info,,

[johngus]

i replaced all my exhaust gaskets in 2021.was not a huge job.I removed all the exhaust.removed the end plates,cleaned everthing and installed all new gaskets.I also services the aftercooler and heat exchanger.wondering if your heat exchanger is leaking?you can probabaly have a radiator shop pressure check it.