I changed all of the capacitors on the tone generator two years ago, because it was getting a bit dull. You can see some photos of the work here. I was pretty satisfied with the result, the changement isn't so dramatic as I thought. The only downsite was that it got a bit to sharp in the highs on a few frequencies. You can get capacitor kits from Goffprof.com
I havn't changed any caps in the preamp, as I think that these old caps sound bether than new one, even thought they may have drifted away from their original value.