I managed to get a spare few minutes this afternoon to sort this. I got a sheet of perspex from a local craft shop, £5.99 for a piece about A4 size. I don't know how good a price that is but I needed to get some and hadn't got time to research it. This is the bit that was causing the problem.

I cut a square out and used my bench grinder to work it into the correct circumference, it worked out very well.

The only problem was that the gear layout disc was a lot thicker than I had remembered and the original cover was quite convex so that it didn't matter that the disc sat proud of the top of the golf ball knob.

Now though I was trying to put a flat piece of perspex over the top so I got out a trusty chisel and took the thickness of the disc out of the inside of the knob.

I had worked the perspex to be just a little bigger than the top shoulders of the knob so it sits in there tightly and job done. It's far from perfect but it's good enough for me and at least the car won't attack me every time I change gear now!
