vacuum power locking

[Snibble]

I am experiencing weird problems with my power locking. I believe that I have a leak in my vacuum lines. When I have all the doors unlocked, including the trunk and gas lid.. and proceed to lock the doors from the driver's door, all the doors lock as its supposed to. However, when I try to unlock, I can only get the trunk and front passenger door to unlock. I have to manually pull the locking mechanicism(sp?) through the trunk to open my gas tank lid which gets annoying. My question is.. where should I begin to determine the problem? What is the most common reason as to why something like this occurs? and lastly, does anyone have a diagram of how the vacuum lines to open and lock the doors look like? I am a visual person, so that will help me out a lot. Thanks in advance to anyone who can help.

Sharif