Hi,
now I understand why one of my boards begins hashing but fails with a short on 12V after 30 minutes:
I will replace them. I hope I find one in one of my boxes. It will hard to replace them with the the backplate heatsink which is melted by thermal activated bonding foil...

I will use my pre heater with low temperature (100 °C) and leaded solder.
Demounting was easy (twist left-right some times). After demontage the chilly works again and has not further an short circuit on the 12V rail any more. So I hope I get it back this evening ;-)
Cheers...
Wow, I can't believe that happened, or that it wouldn't have shorted out sooner.
The best way to solder the new one on is to use an iron, and either solder paste or flux. Clean the pad off, and apply the paste to the pads. Put the new cap down, and just heat the pad and lead until the solder paste flows.