Olympus 50mm 3.5 macro cleaning

[Zamo]

Hi all. I have a thing (part of the inside cever of some piece?) in the inside side of the second glass from behind. This macro lens has only two glasses behind the blades, so it would on the side of the glass that faces the blades. I have removed the first glass (from behind), but cannot take the second one out. There is a retainer ring? with a little triangular hole on a side, but it does not seem to be there to unscrew it.... I think I have to access from the other side. In that case, I would not need to remove the glass, just access it from the blades side... but I really don't know how to get there. So, before starting to open the mount pieces to see if I can do that, I came here to ask. Any ideas on how to get to that part, or how to take out that second glass?
Marked in red, the small triangular dent.


Thank you so much!

[Zamo]

I found this exploded parts diagram https://web.archive.org/web/20161125065752/http://olympus.dementix.org/Hardware/PDFs/50mm_f3.5_Macro.pdf
and the three parts I managed to take off are the marked in yellow here. But not sure how to continue... Any ideas? Taking out the whole mount part and trying to somehow unscrew the whole block?

[sabawa]

https://yossyheim.com/zuiko-macro-50mm-f3-5-repair

[visualopsins]