Why do you think so?
Thousands of RocPro/Performer amps happily out there with the exact same heat sink assemblies (typically somne thick aluminum spreading heat on the whole aluminum panel) .
You have dead transistors, no doubt, but something else killed them.
A common mistake is to unbolt transistors from the heat sink assembly and turn amp on "just for a minute" , "just to check that everything is fine".
That test is usually one minute too long to kill outputs.
Annoying as it seems, board must be pulled to replace suspects, but then must be fully greased and mounted to test.
If you need to repeat everything because some problem remains, so be it
