My best friend is a motor mechanic, history worked at jag and BMW.....
Servicing can be done with any qualified mechanic, and does not affect your warranty, as long as your book is stamped.
He has been very open with me, probably because I've known him so long, and yes I will probably get my z4 serviced for nothing and he goes a step further.
He has serviced my cars in the past and I have never paid more than £125 for a full major service. I know this z4 will be more but not too much.
He is a mobile mechanic and its quite good, because you see him do the work, and all the parts he uses. He has told me really scary stories what people have been quoted.
I looked at my old tyres they were £240 each from a well known place I asked him he got me the identical ones for £87.00 I was amazed