I changed my slave a while ago (last year!!) because the seals had gone and was advised to do the master cylinder at the same time but just haven't got around to it. Anyway I have a few days off and I'm going to do it.
But I also fancy fitting the spring with less resistance (td5).
Is it easier to fit it when the pedal box is out for the M/c replacement? Another part of me is thinking leave the master cylinder alone and only replace when it leaks and just do the spring in the cab

I would remove the pedal box even if I wasn't going to touch the master cylinder. It's soooo much easier working on a bench than in a cramped cab.