Vintage Synth Repair

Hi!

A friend of mine's birthday is coming up and would like to get him a 
book or two on Synth Repair (or such). You know, the usual stuff: how 
to clean contacts, pots, level keys, blah blah blah. As I, he owns a 
few analogs and digital synths. 

Suggestions will be grately appreciated. Thanks in advance!