...so i'd like to share my opinion with you:
If a prewar set is in untouched original condition I would not do anything except a mild cleaning.
I made a sad experience last year with an historical interesting radio I found on a fleamarked. I was great optical condition and the price was o.k. My plan was not to restore it and leave it original condition. When I removed the chassis I could not believe my eyes: Almost everything included the wiring was replaced and messed up in a very poor way. Also many original parts were missing. To make a long story short: I disassembled everything and set up as good as I could with old parts from a junk set in the way it should be. So the set isn't original anymore but in a much more original and better condition as I bought it. I also found out why the set once was 'repaired': G1 of the output tube had no effect even though emission was good. Maybe this was the reason why the set was not used anymore and still exists.
Here is an other interesting story you might like. As far as I heared the vehicle was not restored but cleaned and preserved:
http://www.businessinsider.com/very-...austria-2014-1
Greetings Josef