My 2007 BMW Z4 is due its first service (as indicated on the dash board) and having had a couple of warranty claims, I have had to visit my local BMW dealer twice. Each time they slid my key into a reader and said a service was due soon and would I like to have the brake fluid changed at the same time for approx £75. I realise brake fluid is hygroscopic, but is this just another way to get some extra money or should the fluid need changing? I have never had this on other cars that have done 15k miles in two years.