Trying (and failing) to replace my volume knob!

[wob]

I managed to knock off and lose the volume knob from my E39 basic stereo a while back.

I've bought a replacement from my local dealer, but I can't get it to fit because the shaft for the knob is too far inside the unit itself. I asked the dealer but they had no idea.

Am I missing something, or do I need some kind of extension on the shaft to make it fit? Any help appreciated, as I'm currently having to turn the radio on and change the volume using a screwdriver which is driving me nuts!

Cheers,

William O'Brien