I didn't expect all these responses, in fact I did it because of John Robertson, he has proved the FED 50mm is a gem, that's why I gave it a shot.
The cleaning process is an interesting story, I will find a good way to show to all you guys ASAP, but don't expect too much, my methods are quite DIY, and don't try them on the CV or Xpan lenses.
I will keep all you guys informed ASAP, OK ?
Not quite a photographer.
Current gears :
M6TTL & Bessa T + CV 15, 21, 28/2, 40/1.4mc, 50/1.5, 50/1.1;
Leica IIIf; Repainted Kiev 4A; Fed 1, ...