This is exactly what I have been trying to bring to peoples attention. I feel like I have been beating a dead horse. I hope you all were listening to the video. They "found a small leak in the after cooler" . This is the source of all there problems. This could have been prevented by a regular after cooler disassembling , cleaning, and pressure testing. The blown head gasket are the result of water intrusion , not the cause.
At 75k you have a dam nice sports car in the bilge. In twins 2 cars. Treat them as such and do you diligence and do regular sea water cooling cleaning on a regular basis. This is a common problem in all brands of after cooled engines. If the after cooler leaks you get water into the air intake of the engine. This is the result, a destroyed engine at 3000 hours.
My boat is new to me. An 85 with 2007 engines 1500 - 2000 ish hours I am doing a seawater cooling service, myself. 3200 in charges to ultrasonic coolers, 1150 in gaskets, 1400 in antifreeze. This is for a twin engine setup for a 660 qsm 11. Pluss some metaigneous parts. A far cry from new engine costs.
Take away from this video for anyone with an aftercooled engine. Do your raw water inspection and service on a regular basis. Do not use engine hours. Time is the enemy here. The water in the engine corrodes these parts 24/7 Fresh water flushing slows the process, but only slows it.
If you don't know when it was done last: Just do it. If you haven't done it for a while: just do it. If the boat is new to you , Just do it.
Don't belive me go to smar.com and look up aftercooler disasters.