I have had a trio of lenses given to me a 35, 50 and 90 I sent them all at to Sherry to have them get an upper body cleaning, given the the elements needed cleaning and the mech was still in working condition. She did great work for me, maybe $60 to $80 each. She told me the 50mm was in the worst shape and it would not do well with stray light due to what was left of the coatings, but if I wanted to drop some more $$$ like $190, she would re-element the lens. This was the 50mm colapseable lens, F 3.5 I believe. She did wonders on these lenses. You can contact her at: Dead Link Removed.
The 90 and 35 came out really perfect for as old as they are. I'd feel comfortable sending her anything.
I like that saving money on a lens baby thing for you M camera. I use the not so perfect 50mm and 80% of the time it is just great, just flair and such is a bit much. Before I had them cleaned I took the M2 and lenses, yes the M2 was a gift too, out west and photographed old Indian dwellings. The look was so amazing, high grain film, old hazed lenses, could not ask for more perfect match. I'll have to find some of the scans and post a few, even hazed lenses have great value.
Lee