It always amazes me how people can magically determine the health of the capacitors in an amp without testing or even seeing them. All you have to do is say, "I have an old amp", and instantly there are several "experts" that say "your caps need to be replaced".Get it serviced by a tech. There's electrolytic capacitors that have dried up, so get it recapped.
They must have ESP...
I prefer using the ESR method myself, but that requires actual physical testing...I've never been able to sense that capacitors are bad from 100's of miles away.