ZEISS Tele Tessar f4 135mm HFT - QBM mount help with disassembly needed

Hi,
I am new here, I don't know if this is the right thread to ask, but... I am trying to disassamble ZEISS version (Made in West Germany) version of Tele Tessar f4 135mm HFT - QBM mount... And I cannot get the upper part of upper assembly (just beneath the mount plate, which I've successfully removed) unscrewed. I think there seems to be a thread here, so I should be able to remove it...? If not, then I have no clue how could I remove aperture setting ring. I need to separate (unscrew?) the gray part from the black part to get the aperture setting ring and other parts of the assembly out...As You can see... The other (under/down) side is stripped barebones - I've already disassambled everything I could including the whole fricking bearing (small steel balls everywhere :')) and I really dont see how this side could be disassambled any further.This is not the same as the Tele Tessar made by Rollei itself for SL35 (instead of Zeiss) – that version has another (ring) part between the part which at my age is gray and the part wich is black. By removing that ring (unscrewing it) it allows the whole assembly (part) to be disassambled further, such as can be seen in video by Mikeno62 titled "Sticky aperture blades in Rollei-HFT Tele-Tessar 4 / 135..." if You want to see (around 3:48).

This is obviously not the case with this, otherwise identical lens made by Zeiss in West Germany instead of Singapore.

I tried unscrewing it with as much force as I could (first counterclockwise and then even clovkwise)... Didn't budge.

Please, help. :')
Thanks!
~A.