Hi Peter,
Pretty sure it the inner one, the double convex, though I can't be to 100% sure at the moment. It is proving a swine to get apart. It has had a hard knock in its former life and the sun shade was jammed in the rear position. This I have been able to gently free so it extends to the forward position. The OG lens group is a different story! Stuck fast, a situation no doubt you have encountered more than a few times in your career. I now have red welts where I have tried to unscrew it with a pad of rubber in the palm of the hand for a little extra grip.
Looking more closely I can see both rims of the lens have damage to the outer edges, and they are making some crunching sounds as I attempt to unscrew it. Ehhh!
Any idea's on how to get it apart?
a "Vexed" Bushy
Ps. The OG lens housing is not sitting flush against the tube body so I'm guessing that it has either been screwed in on the "p**s" or been pushed there by the damaging blow.