Thanks. Yes, I think will probably go for a replacement. TBH, we rarely have people at the back so could live with it, but as I need to sort it out for the MOT (due in Feb) probably best to try to sort it out now.
I guess my final question would be whether there are places that would just replace the strap for a new one (and for this to somehow be cheaper than a replacement from the scrapper). The mechanism does appear to be fine and everything seems to be working in order.
Don't even THINK it! Just.... NO!
They're locked on to the retractor drum in a variety of ways, none of them suited to being done by hand, to be honest. The tractor drum then has a long "clock spring" to make it wind the slack in, and that will go absolutely everywhere when you try and take it apart (don't ask me how I know this...)

