There was a thread started by Ipozzo a few days ago about replacing the vacuum pump on a 1990 w124. I know little to nothing about the w124 chassis, but I gathered from the discussion that at some point on those engines they updated the vacuum pump from a open design that could cause damage when it breaks to a closed design that wouldn't. I'm giving thought to replacing/rebuilding the pump on my 1983 300D soon. Did they ever make any such redesigns for the 617 engine and its pump? What should I be looking for on a replacement pump (other than good quality, presumably a Piersburg)? Or could the closed pump from the 601 be backwards-compatible?

Thanks in advance for any help you can give me.