Hi Ian
I have a spare runner with notches in the rubber bit I can send you. PM me the address please. There should be 2 rollers in each runner (not 3!) and there should be stop plates on the mounting bolts so they can not move to far and throw the rollers out. On several of mine there was only 1 roller left and it had got stuck in the centre jamming the runner. The old grease had set to concrete, but with picking the best bits, soaking in the pats washer and using fresh moly grease I have a car set of runners and bits the platers will make fit to use to build a spare set. Onto the next job!
Eric