Get a bias probe and do it yourself.
I took my Marshall to the Fret House in Covina, Ca. It had a "mysterious" problem that was fixed in about 5 days. I'm pretty happy with the turnaround time, other shops said it would be at least 5 weeks before I got it back... But, I got it back in about 5 days and she sounds great!
...sorry don't have the number on me, call info for the number...
...and while you're there, check out the Mesa amp room... the broken windows are my fault...