Nico,
you might try John van Stelten at Focal Point. He is able to get lenses back to near mint condition, he specialises in glass surface cleaning. Fungus might be hard to get out though.
I find the Canon 50/1.2 very easy to work on. I sold one last week that had three aperture blades missing. I picked that up for little cash, but when it arrived ('fully functional lens') three aperture blades were bent and torn! (watch out for ferndowncameras on That Auction Site, used to trade as rockycamera and member....... something as well). Disassembly is very simple, the aperture is easy, and with tightening three retaining rings within the optics of the lens in the correct order, all play is eliminated (found that out on third run, though...)
Seems to me that lenses with even the littlest haze inside flare very easily, but without haze are sharp. I used a previously synthetic cloth and distilled water to clean the surfaces and all came out brilliant, both on the lens I sold for parts and on the black rim one I kept.
Here's a shot with the two side by side:
The little scratches on the front coating in both lenses do not seem to have an effect on the picture quality, now that the internal optics are clean.
EDIT: GREAT SHOTS MFOGIEL, RAID AND JASPER! I really should give my lens a spin this afternoon, once the fog clears up...
