I am the second owner of an '88 560SL, which is in excellent condition and I've not been required to do much self-help work. Recently, however, I'm getting that moaning sound traditionally characteristic of low power steering fluid. I checked and sure enough, it needs some. Problem is the manual only specifies MB power steering fluid; it does not go into the usual "SAE approval", etc. Unfortunately, the nearest Mercedes dealer is 25 miles away and I'm afraid they might not have the right MB fluid anyway. I've been working on cars for many years and have found that using the manufacturer's fluids—which they want one to do for obvious reasons—is usually not required. Further, local auto parts stores have a plethora of power steering fluids and I'd rather go with one of them if there's no down side to doing so.

Can anybody help? Is there an off-the-shelf national brand that can be used in this car? Does anyone know the proper class/spec for the fluid in question?