84 300DT

1. Connected MityVac (MV) on the yellow check valve by the brake booster
2. Door locks are UNLOCKED
3. Pumped MV to 10 inches of vacuum
4. LOCKED the doors on the driver’s side. All doors locked fine but quickly loss vacuum.
5. Pumped the MV to 10 inches of vacuum again quickly loss vacuum.
6. UNLOCKED all doors
7. Pumped the MV to 10 inches of vacuum, NO loss of vacuum

Summary: Doors UNLOCKED – it holds vacuum. Doors LOCKED – does not hold vacuum.

Logic tells me that the vacuum leak is in the INTERLOCKING (yellow-red) line but somewhere in this Forum I read (I could be totally wrong) that the problem is in the UNLOCKING (yellow green) line.

Which line should I proceed to check?

Thank you all for your time.