All the door locks have vacuum bellows and, the driver's door I believe,
a vacuum switch. The leak could be in ANY door, the trunk or fuel door
lock. The last two are easily checked - with your ear inside the trunk
as the engine idles. The doors are an elimination game. You car is the
"right age" for this affair.
Take a look at some on-line parts catalogs to see these parts.
www.thebenzbin.com or www.buymbparts.com