Ian – I have the 501 which is supposedly newer/better etc and having had it apart a few times for cleaning etc it really is a nice bit of kit, except for this one really poor bit of design. That plastic part has an injection point at the thinnest, weakest part of the cage and so naturally it’s here that there is a failure. It’s not a plastic that glues well which is a bit of a bugger, else I’d be tempted to try that.
I have had it all apart this morning into component parts and I bodged a repair, but I’m getting a reluctant take-up in 1st due to not being able to fully tension the pre-load spring (that you identify stu) because of the cracked roller cage.
With a bit of luck I’ll source a spare and we’ll be away. – Thanks for the efforts coatesy!