If you're prepared to travel a little bit, it's well worth the trip to see Steavie at Performance Puma in E18.
I live in Reading and I will happily travel for over an hour for his expertise.
Alternatively, you might like to see Ginger Tom up in Stevenage; he's an HGV technician during the day, but does a bit of work on some very well-known Pumas in his spare time. http://www.gingertommotorsport.com" onclick="window.open(this.href);return false;