I haven't used it myself, but serious vintage guitar restorers use Virtuoso Guitar Cleaner and Virtuoso Guitar Polish.
http://www.virtuosopolish.com/Virtuoso started out as vintage guitar dealers and developed the product themselves for cleaning and polishing high-value old guitars, including pre-war vintage.
Check out their cuctomer comments page, if those comments are trus then it sounds like an amazing product!
http://www.virtuosopolish.com/page14.phpTHey say:
Virtuoso Premium Polish and Virtuoso Premium Cleaner grew out of the need to care for these instruments. Even though they may have been world class instruments, when we got them they weren't always in world class condition. The guitar care products available in 1995 would not clean the finishes without either (a) adding to the grime or (b) damaging the finish.
We set out to find a chemist capable of helping us develop a guitar care system that would allow us to clean years of accumulated dirt and grime without lifting or damaging the finish and also help protect the finish and wood underneath going forward. After numerous attempts and formula changes we arrived at the products now known as Virtuoso Premium Polish and Virtuoso Premium Cleaner. It is the only two part cleaning system designed specifically for nitrocellulose lacquer finishes. It also works wonders on polyurethane and UV cured finishes found on newer instruments.BB