Where can I find info on lens repairs and CLAs?

The following web pages by Robert Monaghan have everything you could possibly want to know about common lens faults, repairs, re-coatings, element re-cementing or just general lens CLA:

If however you are looking to specifically repair or CLA a Leica lens, then aside from than Leica Solmns (who at times can be pricey and slow), John Van Stelten at Focal Point is your man. See his contact details elsewhere in the FAQ.