@Jean Mercier
I would do a serious load test, for example with a 2KW heater. Run it for two hours, that's not a waste of energy in these cold days.
Check the temperature, maybe you have a thermal imaging camera or can borrow one somewhere. It's about the heat pockets, not the overall heat.
Even European electronics are mostly Chinese. However, quality control may be worse or non-existent at Chinese garage "companies". And I'm a bit picky about power electronics, especially in cars.
Electrolytic capacitors are often the cheapest and tend to fail too quickly. If you're clever enough, you can replace them with "Rubicon" capacitors.
Another test would be useful: an electronic power supply or something else that uses a lot of power but is not a resistive or inductive load, but is an electronic load. Run it for a while, turn the loads on and off, and stress it. For example, if you have an inverter, say a welding inverter, take that as a load and run that thing. You just have to pull some useless welds, but so what?
It would be important that you get repeatedly into the overload range, so that the thing switches off. Without a working safety shutdown, that would be out for me.
And it's a good idea to dismantle the housing when looking for heat pockets. Everything above 80 or even 90° C is suspicious.
If no problems occur during all the tests, that should be OK.