G260 how to replace O-ring below input shaft?

[Das Delfin]

How hard is it to replace the o-ring behind the circlip? The realoem diagram shows that a few things I'd rather not mess with are in there but while I'm redoing everything else in the car I'd like to replace that o-ring. Realoem isn't always correct so I'm hoping someone will be able to shed light on the process

This isn't my pic, it's one where someone has (unsuccessfully) applied RTV to the area I'm talking about to get it to stop leaking.

[Das Delfin]

cool so to update this

if you take off the circlip there are (on my car) two metal O-shaped shims and then a press fit freeze plug type device. There is no o-ring replaceable from the outside of the transmission. My guess is that tranny oil leaking from elsewhere gets in between the circlip and metal shims and doesn't ever dry out because it's tranny oil. This makes it look like a leak is forming from that spot but in reality it's from somewhere else.