I think I finally got it out using old school methods.
But what I realized is:
Even if aux water pump is dead, heater still has to blow hot, otherwise there is an air lock.
With aging some hoses or connections might suck some air in.
Now I'm thinking how to retrofit original 105C thermostat to smth with 96C. It will help your engine to survive that stupid 105C heat and all rubber seals will stay flexible.
Any ideas?? I'm thinking of using M54 tstat somehow.
For some reason bmw made it on purpose so engines won't last more than 100miles. Remember first V8 M60? It was 85-95C and no issues with valve stems.