Help me with my laundry list of issues. I've got a 78 240D that I like to keep in mint condition so this is very unusual. FWIW I'm pretty inexperienced working on cars and just learn as I go so go easy on me

1) Vacuum issue. A little while ago I got home and my engine wouldn't shut off. I noticed that with the driver's door unlocked it won't shut off, with the door locked everything works fine. All of the other doors can be locked or unlocked and it doesn't matter. Today I took a vacuum gauge and started checking everything. I pulled the 3 tubes out of the vacuum switch in the driver's door and tested each one. The yellow and green one on the front held no pressure, but the others did. I tested the valve itself and when I put the gauge on all 3 positions it would hold vacuum while locked and not at all while unlocked. Does that mean it's a bad switch? Also when I unlock it there is a hissing noise from the switch. OR, do I need to start tracking down a leak in that yellow and green tube?

2) Locks. They've been working fine until today. I tried to manually lock my driver's door and the tumbler feels jammed. I can lock and unlock all the doors fine with the plungers but it's almost like my key is wrong. Today I unlocked the trunk to get something out and when I closed it, the trunk locked and is now totally jammed. I can't get into the trunk at all. Is this related to the vacuum issue?

3) Fuel burn. Since I bought my car it has consistently gotten 26mpg. I noticed that my fuel gauge was down at 1/4 even though I just filled up and had only driven 180 miles. 12 MPG!! I figured it was the gauge but I put fuel in it and it actually took 15 gallons. My first thought was a leak but I don't see any fuel leaking. Second thought was the odometer but the trip odo seems to be working accurately. Did someone siphon fuel out of my car? If it went from 26 to 12 MPG there would surely be a change in smoke or power output right?

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1978 240D, Daily Driver