Dave, They seem to suffer from bias drift. If you have two or more and they feel (at the fins) to be at the same operating temp, I would say leave them alone. If not, or if they are very hot in use, time for a tune up. Where to go is another story...
How do you know when an older amp needs service?
I'm using Aragon 8008BB amps and they range from about 8-15 years old. How can I tell if they are performing at their peak? They still sound good and they weigh a ton so shipping them in for a check-up would be difficult and pricey. Is ignorance bliss or should I be looking into having them serviced?