Hi, I found this post because I have the same problem. I bought an old lens. It looks very worn :-)
He has sand inside and the focus ring is noisy. I have disassembled the front and back, but I cannot extract the lenses in the central body where the focusing system is.
I think I should remove the focus ring (where I removed the rubber) from the ring just behind. I removed the three small screws, but I can't unscrew the ring despite the presence of the two grooves. By the way: the two grooves are not at 180 ° ... strange.
I fear that the two grooves are not original, but made from a previous attempt at reopening
Can you help me? Thanks
Ezio