It's tough to say really, but I definitely find it cause for concern. I've rarely come across transformers that were designed to run that hot and never in a commercial product. In order to tell if it's really a problem in your case we'd need a lot more information. E-diagnosis of some of this stuff is difficult if not impossible. I'll defer to Dr. Gilmore on this one.
Apparently (after some detective work) my MPX3 is an early
(probably 2004) P2P model. It had two previous owners before me.
No issues have been reported by those owners and I trust their word.
I need to get the amp inspected by a competent technician.
Not an easy prospect here in the UK but I've found several
candidates that are looking good.
I'll update the relevant threads here when I have some info.