Pentosin is a German company, the MB dealer probably gave you the right container. I would have the system drained if you put standard power steering fluid in. I'm not sure with these cars, but the VW's I'v had actually did use ATF in the power steering system and I suspect these are the same. Essentially they require hydraulic fluid, which ATF is a variant of, as is the specified Pentosin fluid. Generic "Power Steering fluid" is mildly corrosive and will destroy the seals in the system if synthetic hydraulic fluid is required. I had a Jetta that someone put normal fluid in and the steering rack seals were all destroyed, which was an expensive repair.