If the dealer claimed they fixed the original fault, they should make it right...w/o additional cost, however, be nice about it. Worse case, they may charge you for some parts, if needed, but eat the labor. You never know.

 

its going back in later this week. They've hinted as you've suggested. So, I'll stay happy and polite and see what happens!

 

They've now fitted a new compressor and charged for it. Seems ok now.
Shame I ended up paying more than a £1000 for a new compressor effectively. Shocking.