I own a 1998 MB S420 and a 1998 Volvo V70. I enjoy doing the normal maintenance to both cars. I would like to keep a supply of the normal fluids on hand to take care of the cars. Specifically, I'm talking about oil, coolant, power steering fluid, brake fluid, and windshield washer fluid. Both manufactures recomment their own brands.

My question is this, Do I need to keep both brands on hand? Couldn't I just keep a supply of one premium brand on hand to service both cars?

If so, what brands do you recommend.