Sam I had an original but scruffy Rexine cover with my WD/L project. Some thinners to remove paint splashes, then I simply used plenty of elbow grease (Which is a problem for me) and black shoe polish. I cleaned the rivet heads as best I could with a small brass bristle brush and painted them with Humbrol black. Just don't wear those gay white trousers for the first few rides
I would have thought that it would benefit from either Vaseline, or some kind of silicone grease applied sparingly, or even a silicone spray., it he reason for this recommendation is that the rexine is quite stable and it's only really the stitching that gives out so I guess that lubricating the stitching with one of the above may help it last longer as it any of them would reduce friction as the stitching stretches and moves around a bit as you sit on the cover
I use one of those waxy leather protectors that an attractive lady in tight leather trousers used to sell at all the bike shows. For some reason, I've never run out. I must've gone back every year.It seems to help with the top but there is no getting away from the fact that the cotton backing on mine is pretty fragile.
I'm thinking of running with one of those gel covers to protect the seat and my coccyx.