From p4cks:

I don't refurbish the gear knobs any more but I appreciate that you and other owners might want to do their own so I'm happy to share the details of how I did it with you so that you can share it with the community.

Firstly you'll need the decal - eBay item number 401577096627
Secondly you'll need some paint - it's Fiat Capri blue and Hycote do a good one
Thirdly you'll need some clear lacquer - it'll need three coats to ensure that the decal does not rub off.

1. Wash dead skin off insert (use toothbrush)
2. one coat of capri blue and allow to dry
3. apply decal
4. apply light coat lacquer and allow to dry x 3

Done.

Good luck