I have a Hafler 9303 power amp and 915 pre-amp. Both have been working fine since 1995. Both equipment have never been cleaned or maintained in the inside since I bought them way back. Is there a need to "maintain" the stereo equipment after so long? I am thinking like dusting, cleaning the contacts, checking conductors are working etc. The "By-pass" switch on the pre-amp pops each time I flick it, and perhaps the contact inside needed some cleaning. There is a hi-fi shop in town that fixes equipment and I am thinking of sending the equipment for "maintenance". What do you think?