91 300SE power steering pump
Pop hood. Locate upper radiator hose. Just to the right you will see the air cowling or air feed to the air filter housing. In between these two and down a short ways is the power steering pump. Has a black knob on top that you twist off counter clockwise. Helps to first remove air cowling, but before you do that, remove air temp sensor from right side(looking at car from front) of cowling. Thumb and index finger depress air temp sensor locking tab, then you twist to remove sensor. Air cowling then easily pops out. With it out of the way, it's easier to get to the power steering pump. After you loosen the black knob on top of the power steering pump a bit, pull up a bit on the lid. It will snap up a bit and come to rest against the knob you just started to loosen. Now finish loosening the knob - remove lid.
Use deep socket 10mm 1/4: dr. to remove 10mm nut, then a plastic spacer and spring. Use a turkey baster to suck out the old fluid. After you siphon out most of the fluid, you'll see the filter in the bottom of the power steering unit. Use needle nose pliers to remove. Have a rag handy to catch residual fluid. Finish siphoning out the fluid with turkey baster. Install new filter, reinstall spring, spacer, 10mm nut. Pour in MB power steering fluid, not tranny fluid or reg. PS fluid. I fill to about 1 in. from top of unit. Put lid and knob back on. Start car and turn steering wheel back and forth a few times. Shut off car. You should have alot of fluid left. Repeat this process with the fluid left in the new qt. of MB power steering fluid you bought. I seem to recall going thru this suction/refill process at least twice, maybe 3 times with a qt. of fluid.
Use the Fast Lane section hear to see photo of PS filter. Local MB dealer or local indy parts house has MB PS fluid. You can buy it from a web provider, but you'll pay for shipping. Cheaper to buy the fluid locally.