Eight to twelve weeks is not that long. The service centre has to receive the amp, put it in line, evaluate it, possibly order parts, repair it and ship it back.
Warranty repair wait times - serious industry problem??
I'm looking at buying a used amplifier that needs some work, and lucky it's still under warranty. In researching places to get work done it's horrifying to learn that it could take two or three months after speaking to a few places.
Is this a widespread problem in the audio gear repair world? That's really bad.