Early (1974) r107 Ignition Barrel Lock

[Isdyl]

Hi, I wonder if someone can help me with an ignition barrel problem please. My '74 350SL has had a sloppy key fit for a while and was regularly not turning. I made the mistake of firing WD40 in the key slot and then I couldn't turn it at all! After following advise on a video on this forum I used graphite on the key and finally it turned and I was able (after much wrestling and head scratching) to remove the lock assembly. I've searched quite a lot for information on how to remove the tumbler and there is a lot on the later ones where there is a hole to poke a pin etc, but I can't see how to remove the tumbler from this. I removed a circlip from around the key entry slot but that didn't seem to release anything, and there is a small spring loaded pin you can see in the photo, but poking that doesn't seem to do anything. Could anyone help please? I don't think the tumbler is available anyway, but not sure what to do at this stage!
Regards, Dylan