I'm the lucky new owner of a 1936 Leica IIIa, and the lens is a little worse for wear. The aperture dial works fine , but it sticks and jams, and it would probably live longer if it was lubricated somehow.
But there's the general warning about cameras and grease and oil, and how some things really shouldn't be lubricated that way.
So, how would I spruce up my lens? I'm probably technically able enough to do what is needed, but I'm going to take it slowly. I'm not going to dive in and experiment.