door lock vacuum actuator question

[kuene]

I was doing door maintenance and hoping to also cross off any culprits in my lock system leak - starting with driver's door in my 82 300D. When I unhooked the 3 lines from the master lock element I was able to get a solid vacuum hold on the right (where yellow with green stripe goes in), the middle (where plain yellow goes) but NO hold at all on the left-most port (where red stripe goes in). I was able to get a vacuum to hold by testing a port and plugging the other two ports.

Here is a picture of what I'm talking about:



When I pump on that left/red-stripe port I get no hold - likes the pump is hardly connected to anything at all. I'm assuming that this is NOT correct behavior and that I need a new element. But one thing I noticed is that I wasn't able to lock the door manually once I had all the lines disconnected. Is this port of the element not going to hold vacuum unless the door is in the locked position? Do I need to do more testing? Or have I determined this element is leaking at this point?

Followup question, when I look on pelican for this part - three with the name "Door Lock Vacuum Actuator, (Master Element)" come up.

One is an MB Part #: 000-800-10-73-M22 - and is $12.25
One is Siemens Part #: 116-800-04-73-M82 - and is $43.50
One is also an MB Part #: 116-800-04-73-MBZ - and is $91.50

The more expensive Siemens and MB ones look more correct in their pic/illustration - but what is that super cheap Benz part that has the same name but is suspiciously super cheap? It has a "Note: from chassis # 036517" appended, while the Siemens one has "Note: thru chassis # 036516" appended.

Can I tell if my chassis is compatible with one of them by the year or VIN? I'm already guessing that since the photo of the more pricey ones looks more similar to what's currently in my car, my question is answered - but I wanted to check before buying. I have a 1982 300D Turbo.

Thanks for any help.