After loads of research would you believe I found a small specialist independent just a few miles away from my house near Stroud.
Family owned, just two guys and a lady, been doing VW transporters for over 22 years and specialise in campers so they can sort other issues as well.
Happy to use VW parts to keep your warranty intact. Yesterday they did mine - full service, mot, cambelt/water pump and all the ancillaries. Really nice people and they know what they are doing.
if you want to talk to them here is a link, they have courtesy cars if need or it’s a short walk into the town.