Blimey, that was a bit easier than i thought. The door just moves up and down on slotted bolt holes. I was imagining having to to move the rollers and stuff like that.
Door opens and shuts nice and easy now, can't get it to bounce back open, and also i can't push it open from inside by just leaning on it

Shut lines are about spot on too. Proof will be in the driving, especially speed humps. But signs are good.
The latch seems to still be square, there is a bit of wear on one bit of it where the strike bolt wasn't lining up but this doesnt seem to be affecting it.
So, cheers for the link Micky

And cheers to MM for posting in the first place
p.s. Also found no rust under the runner cover

just some paint flaking
Time is a drug. Too much of it kills you