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its a diesel, it doesn't have vacuum lines.
You can find a vacuum hose routing diagram for a 1988 Mercedes 190e 2.3 in the owner's manual. You can also find it at various auto part stores.
You can find a Vacuum hoses diagram for gm diesel 6.5 at any department stor. They can be found at Sears or auto motor store. They are also available on Ebay for a bid.
I have spent a month looking for this with no luck...
Ebay occasionally sells a CD with wiring and vacuum diagrams.
http://www.peachparts.com/shopforum/diesel-discussion/215532-vacuum-door-locks-not-working-1983-300d.html
It is in the rear of the timing cover below the injection pump and above the vacuum pump.
Diesel engines do not have enough vacuum themselves
Google search - 351M vacuum diagram
vacuum line diagram
A gas engine produces its own vacuum, where a diesel engine has to have vacuum artificially produced. Your transmission problem doesn't sound like a vacuum problem. Have you checked the fluid level? When was the last time you changed the transmission fluid filter?
7.3 Diesel has a vacuum pump.... belt driven