I have often used Febi PS fluid which is supposed to be the same as the MB, but the MB fluid from the dealer should cost only $10-12/quart, versus $6-7 for the Febi, and you can blow your savings searching for the Febi (which I get at BAP). There is a filter in the bottom of the reservoir - remove the top nut, deep 10mm socket I believe, and pull stuff out until you find it.