I've a retro fitted vernier isolastic set up on my 1972 Commando and the front rubbers have a split. They look like they "may" have split because they are a tight fit to the frame, but they are 12 years old so I'm not certain. Looking at replacements I'm not sure if I need the MK111 type as they were verniers or the pre Mk111. Any clues. TIA.