As a quick check, Paul......whip the Rekord out of your 95 and try it in the 35. If that does the trick, job done, sorted!
If you were still to encounter the non-cocking issue, it could be a few things.....yes, that damage on the piston slot not allowing the lever to push it far enough rearwards, or it could be that, in combination with this, the cocking lever is slightly bent. You can get new ones quite easily....I think I paid about £22 / £23 last year for mine from Bagnall and Kirkwood. I think Knibbs have them, too.
A request for help on the forum should net you a replacement piston. I wonder if yours is the earlier type (with a leather to synthetic adaptor fitted) or if it has been replaced with the later type for the synthetic seal which is lighter and gives more stroke?