If going the RSC route I would take the watch in person if I was you as you can detail what you require in person and also you have the confidence that it’s in the system and in safe hands .
I can’t see an issue it being on a Rubber B .
I think it would be around the £600 mark ( subject to parts ) but service prices have gone up and this could be a fair bit out .
I think you could get it serviced independently but it won’t
( as far as I’m aware but could be wrong ) be able to be pressure tested to the full capacity.
Look forward to the comments of others and great watch BTW and massively underrated and valued in my humble opinion.