I hear this so often, because a garage can change a set of plugs on a Fiesta they think they can do anything. I have had Interceptors delivered to me on a low loader after a garage cant get it going or no brakes. Specalist cars need specalists and trying to save a few quid by taking somewhere local or handy is often a bad idea.
If it was me I would bite the bullet and send it up to Chris to sort it once and for all
1958 Ford Consul Convertible
1965 Ford Zodiac Executive, being restored
1997 Jaguar XK8 Convertible
2003 Number 182 MGZT V8
2004 MGZT cdti Poseidon
2004 Number 76 MGZT V8