If I were you I would try Charlie Priaulx-Wells at the SEC-Shop. Based in Kemsing in Kent, not too far from the M25. Really a good mechanic and has a personal thing for all SECs. I have used him extensively and he takes a personal pride in getting the cars 'right'. Having said that, he is overworked and accordingly catastrophically disorganised. He had mine for nigh-on 2 months at a stretch this year and it was always going to be ready 'at the weekend...'
He had the boot repainted 5 times before he was satisfied with it though.
Also, honest as the day is long... which is tough to find. On balance I have looked far and wide and he is the best for SECs - they need a real specialist.
See sec-shop.com or call 07970 553071