I've been going to Portsmouth/Southampton 4-5 times during the past few years and have the following garages noted for any work on the 75 when in the area.
MJSMarine in Littlehampton used to come highly recommended on the forum.
http://www.mjsautoandmarine.co.uk/
Also, Gregory's garage in Fareham.
https://the75andztclub.co.uk/forum/s...ad.php?t=66376