Pete, I also have a 91 525i and was trying to figure out what type of p/s fluid to use. The cap indicates the type of fluid used in your car. My car has the "chf 7.1" (I think that's the name) You will not find this at local parts stores. I found some listings on the net but got better deal from dealer w/cca discount was about $16 per liter. My car has a manual trans but requires ATF as lubricant I use Mobil 1.