Here are some vacuum diagrams to help you diagnose your W123, W124 or W126 diesels. The 240D diagrams were looked up for a 83 year model, but should be pretty much the same for 82-85. I've also added some wiring and flow diagrams. Also note that there are year to year (and sometimes, throughout the year) changes and these diagrams may not reflect everything exactly as on your model.

'86-'87 300 SDL, '87 300D vacuum diagram


Cruise Control Repair Articles
http://www.peachparts.com/shopforum/diesel-discussion/123036-cruise-control-repair-articles.html#post883130

Diesel Vacuum system adjustments
http://www.mercedesdismantlers.com/diesel_vacuum_system

722.3 and 722.416 transmission adjustments
http://www.mercedesdismantlers.com//722.3and722.416_transmission_adjustments.html

722.118 Transmission Adjustments
http://www.mercedesdismantlers.com//722.118_transmission_adjustments.html

Diagrams for W124.128 with OM602.962.
http://www.peachparts.com/shopforum/groups/w124-300d-2-5-turbo-pictures.html

OM603 Vacuum & EDS Diagram
OM603 Vacuum & EDS Diagram


Edit:http://www.peterschmidtransmission.com/vacuum.htm also has a good deal of vacuum diagrams available.
http://peterschmidtransmission.com/mb_files/vacuum_schematics.asp
Vacuum Control Valve Test:
http://peterschmidtransmission.com/mb_files/vacuum_test.asp


1985 Mercedes Benz 300SD ACC Vacuum Diagram
http://autorepair.about.com/library/images/bl929lib.htm

(W123) Fixed vacuum leak, now tranny flares
http://www.mbca.org/forum/fixed-vacuum-leak-now-tranny-flares