3rd new heater core leaking - caused by heat? 2001 Caravan

On a 2001 Caravan (3.3) I initially misdiagnosed a bad heater core (coolant in the air plenum). Turns out a gallon jug of coolant sitting on the floor at one time splashed up there. But, I pulled out the old core and replaced it. I tested the old core and found no leaks, but replaced it with an aftermarket anyway. Two weeks later, the new one leaked at the joint between the tank and the core (plastic to metal) even at lower pressures. Pulled it out and went to reuse the original and lost an issue with the o-rings and assembled with a non-OEM o-ring. Leaked at the o-ring. Got correct o-rings for $23 at Dodge, continued. Went to reinstall and see in my messing around I had cracked the tank flange. Got a new core. Installed, 2 weeks later it leaked (same place). Put in another - same thing. Cap is good. System pressurizes into overflow tank and sucks back in. System flushed.
So… this time I tested the thermostat and found it to be bad - never opens. I don’t drive the car - belongs to my son - so not sure what the thermostat read on the dash but here’s my theory:
New core uses marginal parts (you can’t buy OEM cores unless they are NOS - they stopped making them in 2020). Occationally, due to the thermostat not opening, the car overheats. The higher temp causes the seal between the tank and body of the heater core to fail - a deformed gasket, or maybe they use some kind of glue that fails at a high temp.
Does that sound plausible? Naturally, I’m going to replace the thermostat, but debating if I want to pay for a NOS OEM core on this beat up 2001 Caravan.
On the upside, I’m very good at replacing these now. Book time is like 7.5 hours and I can get it done in 3.

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Suggest to ask at your local repair shops & parts stores if anyone knows of a good radiator specialty shop. They deal with this sort of problem every day, and will know what your best options are.

Do you test the pH of the coolant regularly? If not, good idea to adopt that habit. Best to not allow the pH to go less than 7 - 7.5. The more the engine runs, the more acidic the coolant becomes. Eventually the acid will start metal corrosion and damage the seals throughout the entire cooling system.

I don’t think I’ve considered a radiator shop in ages since they all have plastic these days, but yeah I’ll check that out.

Definitely not corrosion - fluid totally clean (flushed, replaced) and this is happening within weeks. Also, no head gasket issues (no exhaust in system).