Mercedes Diesel Mechanic working on my car. What else should I have him check?
 

Well I will be having a very knowledgeable Mercedes Diesel Mechanic fix some issues with my car.

It turns out he lives only 10 miles away.

I will be having him fix my A/C it doesn't blow any cold air at all. Also the heat doesn't work.

He also will be fixing my Locks and my issues with the transmission that seems to be very common with this car.

On my own I have with guidance from my Uncle

Changed Oil and filter,did a diesel purge,Changed transmission fluid and filter,Purged P/S Fluid and changed filter,Cleaned the coolant system and replace the proper Antifreeze. Air Cleaner Filter

Changed all fuel lines and went to Biodiesel safe lines. Changed all Fuel filters and installed Standyne Filter also.

Later on I would like him to adjust the valves and replace lights in the dash cluster. But what else would you recommend?

Check the chain while he's doing the valves.

Sixto
87 300D

Just my opinion, but I wouldn't pay a mechanic to troubleshoot the vacuum system. I think you're better off using the resources on this site and a Mity Vac and figuring out how to do it yourself rather than pay a mechanic $90 per hour to troubleshoot the vacuum system which can be time consuming. Given everything else you've done it seems you are capable of doing the vacuum work.
On the other hand, fixing the AC system can require specialized gauges which a lot of people don't own.

Is there enough slack in the oil pressure line to pull the cluster out enough to change bulbs? Seems like something a DIYer should be able to tackle.

Sixto
87 300D

Kerry...Thanks for the compliment. I really haven't had any other car of this age. I have owned used cars but none have made me want to do the work as much as this one. This site is the only reason I was able to accomplish those tasks. I really think the door lock thing I could do but he will be working on the transmission vaccuum so I figured I might as well have him work on that also. The locks are very important since I have only let himdrive in it once. I feel for saflety I need the locks. My 3 year old son loves to sit in my lap and steer the car while I drive up the driveway.

IMO the transmission adjustment is over my head.

sixto I might tackle the dash by myself. The RPM gauge doesn't work is this something I can do while I'm in there? Also I will have him check the chain.

On a 123, there is indeed enough slack.
While he has it out, he can unscrew the back, and paint the insides (of the little cubicle that the bulb sits in) with white model paint.

Tach problems rarely involve the tach itself. Behind the driver side headlight there's a cylinder a little bigger than a 35mm film canister. The tach amp is inside that canister. Do a search on methods to get the tach amp working again. Typically what's done is - pry the circuit board from the canister top, stuff a foam peanut or cigarette butt into the cover, refit the circuit board, put the top back on the canister. What the foam peanut or cigarette butt does is press the board pins firmly into the connector. 9 times out of 10 that will get the tach working at least long enough for you to find another foam peanut :)

Sixto
87 300D

The transmission vacuum problems could easily be a result of problems elsewhere in the vacuum system. Fix those and the transmission may be fine. You can simply plug the door portion of the vacuum system and your transmission might work. The door locks will all work independently of the vacuum system so there shouldn't be a safety issue with them apart from the fact that you have to remember to lock and unlock the doors manually. Humans managed to do this for many decades before vacuum locks were invented.
Personally, I would make no adjustments to the transmission vacuum before resolving the other vacuum problems.

yup.
block off the bright yellow vacuum lines, and see how it drives.
if it's fine, all you gotta do is follow the 6 pods and check them for vacuum flow...
you mention a/c issues... this could also be related to cracked vacuum lines... the pods are controlled by the vac manifold under the passanger's side console... fun!
does the a/c compressor come on properly and get cool freon to the return line? (the line going to the compressor from the cabin, not the one going to the front end of the car.. it will be VERY hot if the compressor is running DO NOT TOUCH IT!!!)
and the tranny if it needs adjustment, there is a nice thread here explaining in detail how to test and adjust the vacuum on it. search for transmission critical vacuum or something like that. or just wait, the thread will pop up here shortly... it usually does.