If the engine has to come out, as it will for a stator change, they should be able to change the Centa rollers for just the price of the parts, about £35 for a set of four. There is no extra work involved in replacing them, other than carrying them from the stores to the car 😁.

As stator failure is so rare on the M3W, it will be interesting to see just what the problem is with the stator and what they think has caused it. I would ask for photos or to be shown the indication if there is no visible break in the wires.