2007 ML320 diesel
My transmission went catastrophic November 1, 2021. I have it to a local transmission shop and not a Mercedes dealership for obvious reasons. During the course of that year it placed in my car 3 transmission that went boom on the lift. I suggested changing the radiator. It took months to get on in an with a another transmission it ran great for 6 months then died again. I gave it back to the shop since this is a warranty issue. They finally got another one in this week and boom. Another one failed. The shop is pulling it's hair out my wife is pissed and I am at a loss. For reference, lines have been purged and software updated. The shop did a lot of work trying to troubleshoot this issue. I have to ask has anyone seen or heard what could possibly be causing this? It's going on year 3.

Could it be the engine thermostat? Not having any heating issues.