pentax 67 light meter weird issue

hello photrio
i have a weird issue with my rather excellent condition pentax 67. i am using an old ttl finder from the first generation (6x7) and until recently it worked fine.

what i experience now ist that its metering fine without lens on, or with the takumar 105 on (although only in manual mode, if i switch to auto the needle drops, no metering).

but, and this i do not understand at all, since a while already i get no more reaction fron the light meter as soon as i attach one of the pentax extension tubes and i cannot figure out why. this hasn't been the case before and i wonder.. batteries are fresh
any ideas?
thank you.
chris

update:
solved the issue.
the little pin on the camera mount that deactivates the ttl meter is a tiny bit longer on this body (i have two, no issues with the other one) and using a tiny drill to make the little indent on the tubes just a little little bit deeper so that the pin can fully extend solved this..
in case this is helpful to somebody else.
cheers

Thanks Chris, I have a 6x7 MLU and 67, neither seem to want to meter with the Pentax extension tubes. I'll take a look at these pins and the tube mount.