Any compression over 300 is fine. Sounds like glow plugs. You mention one is already out so I wouldn't be surprised if the others aren't far behind. One way to find out for sure is to pull start it. MB automatics have a rear pump so will start.about 30mph and put in drive. may take 1/4 mile or more but should start even if your injectors are worn. Worn injectors WILL cause hard starting. There is a wealth of info from a fellow with a shop in Northern Washington state. You can type in mercedessource (his internet name) He also posts videos on u-tube for DIY and explains ( in detail) how to fix things on these cars. Does this car have a block heater? Try plugging in for hour or 2 if it does have one

 

Well I sat on on it too long and someone else bought it. Apparently he got it running and from what I heard is that it was just the timing was off.

Thanks for everyone's help and suggestions.