Yes, it is/was. Not sure if it was really rubber, but it was some flexible material, and it does go sticking after a number of years. The problem (beyond clogging the type cylinder) is that if the stud on 180540 that 180502 goes on to is exposed, it will damage the surface of the type cylinder. I wonder if you could cast one using that stuff that classic car restorers use to make rubber parts [an aside : Anyone know where to get that in the UK?]. Making the mould would be fairly easy, I think.