Use the ignition key to lower the rear seat.
Remove the plastic liner in the pass through
remove the half dozen or so bolts holding the plate the pump is attached to .
lift the entire assembly up and rotate upside down. Fluid should be between the 2 fill marks on the plastic reservoir. If not, 13 mm bolt comes out and you can fill it.
As to fluid. I read all that I could and researched the information from the pump OEM supplier (Power Packer) . The same pump is used in several European brands and they indicate that all the fluid is the same from brand to brand but are dyed differently. I can't attest to the accuracy of that but I have used MB convertible fluid with no ill effect. Saab was out of stock with no expected delivery date. About $50 a quart when in stock. The Mercedes Dealer charged me $18.00 (shop rate).