Just to add my RCR horror story.
I am happy to do my own maintenance and running repairs, but I took out RCR when my son and daughter-in-law were using our motorised butty. They broke down at Braunston and the RCR engineer diagnosed a faulty injection pump because the engine would start and then cut out. To cut a very long story short, the RCR fitted an exchange pump but the problem persisted. In the end I said, "Forget it, we'll sort it out ourselves." Fortunately, we had the motor with us so we were able to tow the butty back to base. There a proper engineer, Ed Boden, correctly diagnosed and fixed, a blown cylinder head gasket.