They are all there for either TT builds or customers wanting to upgrade their existing TT cars to a higher specification kit (there are also a couple there getting kits from other builders swapped out for a UGR package). I don't see them doing much normal "maintenance" there, unless the car happens to need it while it is there for something else or the owner is semi-local. The cars typically can be serviced by whomever you would have trusted to service it stock.