An update to my previous post re blowing a radio fuse while trying to check out my faulty CD which may be of help :
( BTW Thanks to Jac and Pewe for their advice)
The blown fuse ended up being on the power PCB on the rear of the radio - there are 2 surface mount type of 6.3A fuses here. Not sure how I managed to blow that!
I had to solder in an inline type hanging off the board - not elegant but works OK. While I had the radio out I decided to risk the C101 / 102 mod described by Justin to improve the awful sound. The caps are quite easy to get to - Take the front fascia off ( screw either side ) and then pull away the bottom of the casing - the caps are on the underside of the PCB.
Glad to say that this has made an enormous difference - Not only some actual treble but it will now go quite a bit LOUDER!
Those darn caps are just shunting alot of the signal to earth.
However, I would repeat Justin's warning - unless you have some experience working on surface mount PCBs then leave it - The surface mount caps are tiny - I very nearly chickened out but decided to go ahead as I had an Alpine unit in the wings if it all went horribly wrong.
I also discovered what was causing the err3 on the CD - It loads fine but doesnt rotate - Not helpful!
Anyone got a CD unit for a 95 GS300?

Dave