OK, I've been researching this topic for a while and ended up stumbling across an answer from Honest John, who recommended someone for Transmission servicing in Surrey - King Automatics (
www.kingautomatics.co.uk).
I sent an email enquiry and got a reply from a different garage in Wimbledon. He said this was their new name. (
www.wimbledonautomatics.co.uk) The guy really sounded like he knew his stuff - he knew to use the correct LG fluid. He quoted me £270 to change the fluid and filter in the S8. When I enquired about the sucky/blowy thingy, he responded that the machine works by adding pressure at the cooler line to flush the fluid through. He was happy to do it for an additional £70 (IIRC) to cover the additional fluid required.
He said it would take a couple of hours for the Volvo and a little longer for the Audi.
I should point out that he quoted me a cheaper rate because I wanted to have both the Audi and the Volvo done.
Has anyone heard of them/used them?