I have a 1980 Mercedes 300D. The climate control servo leaks badly until the engine heats up. In addition the fan does not operate but heat does come out of the defroster units. I've read that these units often fail. A replacement is 475 used and about the same rebuilt but I'm told that the rebuilts don't last. I'm thinking of getting the digital conversion. Anyone have any experience with a digital conversion?. Is replacement straightforward, does it function well, and do these hold up over time?