I had this done at 75k miles by this company in Aylesbury:
https://www.staautogearbox.co.uk/
I got a company to do it as I don't have ramps to keep the car level, nor do I have an infrared thermometer to do the refill properly. This company also uses a machine to pump or suck all of the old oil out rather than just letting it drip out.
I asked them to do the mech sleeve but their feedback was that it looks good and dry. They also checked and topped up the rear diff too.
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2016 435xd GC, MTC intercooler, centre and back box deletes, GKR stage 2 remap, methanol injection, H&R lowering springs. To do: wash it.