You simply need to see that all steel surfaces, inside and out, are clean and treated with a film of lubricant. I like Ballistol for old guns because it is completely safe and harmless to any finishes and it treats the wood. You would want to clean the bore with it on a bore brush and finish with a patch. Corrosive ammo was used in Lugers and they were not always cleaned after use, so the barrel may be pitted. While affecting value, this does not diminish accuracy or shooting fun. If your bore is smooth and bright, that's a big plus. This will be viewed as controversial by some, but it's a fact nonetheless - you can actually immerse the gun in Ballistol without disassembly to make sure every surface is lubed, then drain/wipe off/blow out excess. The gun is then stabilized but should be stripped and manually cleaned before firing or long-term storage. The latest gun I did this on is a 1918 Colt M1911 that had not been cleaned in at least 40 years. I later detail-stripped it which was a lot easier than a dry gun that usually has some light rust in tight places. The Ballistol had liquified most of the dirt and rust by that time and aside from the bore brush, the most aggressive tool I used was an old toothbrush. You don't have to immerse a gun - you can do basically the same with a spray can, but you have to at least field-strip it.
It's wise to fear messing up an heirloom gun by taking it apart, but there are many excellent illustrated manuals and videos on the subject. First learn to field-strip, which amounts to removing the 'cannon' or upper half. This may be as far as you will go, and is adequate for general cleaning.
It's been years since I had a Luger, but now this is making me want another. Why did I come back here and read this?
