I have conserved a couple of old guns, the most recent being a SA 1884 Trapdoor that was on the wall of a barn for the last 50 years. The wax I use is Renaissance, expensive but right (about $30 for 7 oz.). It is a micro-crystalline wax specifically designed to provide long-term protection to wood and metal. Do not oil the gun after cleaning, but give it a light coat of wax paying special attention to corners and sharp edges.
For cleaning, I use fine bronze wool with WD-40 (sparingly), then wipe with a dry cloth. This is only to remove the surface dirt and rust. This must be done very gently so as not to disturbe the old patina on the gun or any of the original finish.
If the gun is particularly collectable, and appears to never have been "detail stripped", I do not dissamble it. Otherwise, I completly dissamble it for cleaning and preservation. In cases where there appears to be internal corrosion, I might resort to vibratory cleaning the part in crushed walnut shells, then wipe clean, wax and reassemble.
I shy away from "restorations", as I think the results look like old guns that have been scrubbed, varnished, and reblued. That may be fine for guns used by "re-enactors" or that will be shot in "old-time" or "antiques" matches, but for family heirlooms or collectables, the less you do the better. Lean toward preventing further decay and away from achiving the NIB look.
Hope this helps...
John R
Seneca, MD