If that amp has been sitting in the closet without being played for years, despite the fact that it works and sounds fine now, every electrolytic cap in the amp needs to be replaced. Most quality electrolytic caps made today last 10-15 years with optimum performance and the old caps were not as good. They start to degrade over time, and especially with non-use. The electrolyte paste inside the caps dries up, and causes the cap to not function as well as when new, eventually the cap loses it's ability to filter the hum out, or will physically leak the paste out, etc. If anyone was going to buy the amp, they would want to replace those caps first thing for reliability reasons. If you wanted to sell it for a higher price, depending on the buyer, replacing the caps could bring a higher or lower price. Just wanted to give you a heads up as it is one of the things that will come up when you try to sell it.
Greg
