One of the best seller i know is "g-comex".
I have dealed a few times with him.
One of his auction is a gen 1570 GMT movement with silver date disk but closed 6+9:
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=120473511193&_rdc=1
Yes, the ring is the key.
I have had the same problem on my 1665 and a tropic 39.
The crystal fit the case, no problem, but you need to sand town the ring that come over the crystal.
Hi,
you can polish it out with diamond paste.
I have tried it a few times and it worked.
If it is hardened mineral glas you can polish it out with 1,5 micro meter paste.
If it is saphir you go a little higher with the grain and take 2,5 micro meter paste.
The nope was in his workshop and have tried a few gen ETAs.
All the same stems. 2834-2, 2824-2, 2836-2.
After that the nobe was calling his friend. His name is Domi.
He said that the 28xx have all the same stem, without the 2892.
And now...?
Sure it works.
I have polished 2 bad and deep scratches out of a saphire crystal with a Dremel and a diamond paste.
And it depende about what grain you take.