Well I got the part and installed the new MAS.
The MAS unit (122) is bolted onto the intake air filter cover on one end, and connects to the hose (127) going into the intake manifold on the other end.
A simple job: Pull out the electrical connector. Loosen the screw on the o-ring clamp (133). Open the air filter cover so you can twist the cover/MAS unit away from the hose. Remove the 2 screws holding the MAS to the Air filter cover, then pull MAS off. Remove, clean, and re-insert the the rubber seal ring (114) on to the air filter cover. Screw on new MAS. Insert open end of MAS into hose. Replace and clamp down the Air Filter Cover. Tighten the o-ring clamp to secure the connection to the hose. Re-connect the electrical connector. A 10 minute job done in 20 minutes.
Rather than waiting for the Check Engine light to reset (which probably takes a week) I drove to the local Autozone to have them Read and Erase the OBD2 code. The guy there knew only how to Read the code, so he thanked me for teaching him how to Erase. Heck, all I did was pointing out the Erase button on his tool!
I hope the attached image makes it clear to newbies like me DIY for the first time.
84 300SD sold