[bojan]

Today, after a lot of anticipation, the lens arrived....
But it was a disappointment.
I didn't mind the external cosmetics, neither the interface to camera (which was stuck BTW). I intended to use it for astrophotography only, so modification to EOS was on my mind from the start.
When I had a look inside against the sunlight I saw the lens have extensive damage caused by fungus and moisture on the back of focussing element. Ouch..
And then I made a biggest mistake of all: I started to dismantle it to see if this fungus can be cleaned...
And then I found out someone attempted to clean it before me and even did not properly assembled the affected element so it was loose inside. Retaining ring was loose and visible as that from the start.
The lens was not really functional when arrived, but I can't prove it now..
Focussing element (7-th from the left on attached optical schematic) needs polishing on back side, it is negative doublet, 70mm dia and 18mm thick.

So, question: where can I polish this surface, or, where can I obtain cerium oxide to do that myself? Are there any mirror-makers left around?
I did polish mirrors in the past, so.. maybe I can do it again?

The front group looks OK (just a tad of fungus on the back of the meniscus, 6-th element from the left), and this can be probably cleaned with windex and dishwashing detergent, no big deal at all.