Would like to ask if doing a CLA will destroy the L seal on the camera body (earlier M series).
-> Yes, there is a screw under the seal. It is kind of warranty stamp in electronic stuff nowaday
I vaguely recall that it is possible not to destroy the L seal from one of the websites I read.
-> No, but L seal can be faked. It is just a stamp anyway. It is not difficult to fake. One local repairman once told me he could do the L seal
The only way is to send to Leica to do CLA for it to be intact?
-> No, Leica won't seal it again. They stopped doing so.
Well, in my opinion, L seal is just for some people who wants a "virgin" collection. In fact, most people who use camera to take photo, would prefer camera with good CLA to a old camera with seal.
Beside L seal, there are many different seals from other good CLA services (DAG, Sherry Krauter, etc).