If you are doing approx 40k a year in the car would you agree its not going to be worth much anyway when you come to sell it. It'll be a three year old car with well over 100k on the clock which will devalue it considerably.
Most people buying a very high mileage car won't be too fussed if the additional service bits were carried out independently as long as you have proof of original BMW parts - so that could at least save you some cash
It seems strange to me that prestige car manufacturers let such complete idiots run their dealerships. I mean the cars sell themselves so you could theoretically have a monkey in the sales team. The service side is usually awful. I mean a lot of BMW owners accept they are going to be shelling out for ownership costs but then you expect a degree of service for that price that is better than most other places.