This is an interesting write up on the subject.
I am yet to flush my transmission on a '12 v70 D5 with 120k miles on it, but did the EDT for engine oil and oh my, the engine came to life! Revs were faster and the whole car livelier. I've done it in Basildon's EDT branch near work, not Hortons but considering them for the transmission flush as the Basildon garage doesn't do it.
https://hortoncars.co.uk/volvo-news/...and-solutions/