Ok finally managed to find some time to update this.
Tom and stormcloud - thanks for commenting on this thread. The MX is a great camera. It's a little bit before my time also, but I love using the older gear.
Unfortunately at this stage I am missing a couple of photos. Repainting the film door was difficult for me, as I'm really not a good painter! But this is what I did:
1. Bought some black gloss spray paint, specifically one I could use on the metal surface of the film door without a primer. If you would like any further details on exactly what I used, let me know and I will find the can. The paint type is enamel.
2. Wet and dry sandpaper. With this I carefully sanded down the worn areas in preparation for painting
3. Repainting. I actually didn't spray the paint on - instead I used a small soft brush. Possibly not the best method, but I am happy enough with the result. Painting the whole film door was not necessary, as the new covering would cover most of it.
After two coats the paint job was as good as I was going to get it - by no way perfect but a lot neater looking than how it was originally!
Before I get too ahead of myself, I must mention the film reminder that you can see on the back of the camera. From factory this film reminder has it's four little feet melted (OK, minor assumption here) into four appropriate holes in the back of the film door. When I removed the rear leatherette and prepared the film door for repainting I had to remove the black plastic film reminder. It came off easily enough but the holes where the feet go actually goes through the light-proof film door!
This seemed like a potential issue at first, but then I realised two things.
The first is that the film pressure plate that holds the film flat looked like it would block the holes when film was loaded. My second thought was that I could just carefully 'Supa Glue' the black plastic holder back in it's original position. Thankfully, this worked like a charm! No light leaks, film reminder securely in place.
Back to the camera covering - the fun part!
I installed the rear covering much the same as the front, wetting some parts of it slightly to slow the setting of the adhesive. If you have read through Jon Goodman's (the friendly 'interslice' seal kit guy) camera seal kit instructions before, you may have noticed that he mentions licking the adhesive for mirror bumper foam before application. While there are some suggestions on the camera covering seller's website, my method was the one recommended by Jon. As is commonly said here on PF, Your Mileage May Vary - but that's what I did.
Recovering the rear film door went fairly smoothly, and now the camera was just about complete. Here are two photos of the edges of the film door that I repainted:
...
Now finally I can show the finished product!