I don't know of a repair shop closer to you. But you don't have to send the whole console. You will have to disassembled it. Looking at the Owner's Manual, it pictures the Power Amplifier unit as separate from the radio/control unit. Look at the backside. Some units, you could see right into it. Some had a cover. The power amplifier is in there. Remove and send that part. The hiss and buzz could be coming from the top radio control unit. That unit takes a bit more to do to remove.
Consoles like yours is how I made my first stereo system.