man, that radio is 15 years old and you don't know if the previous owner messed with it! so, my suggestion is to buy a new radio!!

 

It sounds like you've troubleshot an intermittent open circuit condition most likely to be in the power or ground inside the radio chassis. If you are set on saving the old radio I'd try cleaning the pots with some of that pot cleaner stuff electronics stroes sell. If that desn't work open it up and check for operation by powering the thing up and jiggleing stuff until you find the the thing that when wiggled causes the intermittent condition to change state. Then just scrutinize and fix that part, likely to be a wire or solder joint somehwere.