I would flush the radiator changing our your old fluid. No damage can be done by changing the fluid too much, a lot of damage can be done by not changing the fluid enough - my wallet learnt that one the hard way. Also every 50,000 miles why not flush your transmission, not a drain which is what most places offer, but a flush. A drain will only remove about 60% of transmission fluid, a flush removes 99% of fluid.
Oil changes - at least double the number of oil changes recommended by BMW and your engine will go one forever - okay, I exaggerate but it will extend the life of your engine.
And now for a kinky one - if you want to clean deposits off of the walls of your engine, change the brand of gas every 5000 miles. For example, use Chevron gas for 5000 miles, then Esso gas for 5000 miles. Each brand has different additives, in fact the gas may all be from the same company, but each company adds its own additives. In Vancouver British Columbia, almost all gas sold through different companies is Chevron gas, but each company adds its own additives.
So the additives of Chevron gas will remove "foreign" deposits, but eventually build up its own deposit. But by changing your brand of gas over time, the new brand sees the Chevron additives build up as "foreign" and will remove the old build up, but will slowly create its own build up. Then after 5000 miles switch back to Chevron and the process starts all over again.