Ford F150 - 88 F150 Brake Problem

I just "inherited" a 1988 Ford F-150 4x4. It has been sitting for about a year or so. All in all the truck is in decent shape with the exception of the brakes. When i press the brake pedal, it "creeks" and then gets stuck down. I have to manually pull it back up as it "creeks". My uncle said the truck has had this problem as long as he has owned it. It only does it when it's not used. He told me to spray WD-40 on the pedal and it will go away. I tried n tried.
I would rather fix it the right way to avoid future problems. If i get under the dash and look at the rod that goes through the firewall it seems rusty. Is the booster the issue or is it the pedal itself? I am unsure what the rod is a part of the booster or pedal. Thanks in advance for the help.

Yes, the rod is part of the booster, not the pedal.

If you're getting normal brake operation when you press the pedal, I don't think your looking at a vacuum leak. It may be the return springs inside the booster are damaged or there is some other sort of mechanical defect where the rod passes through. But either way, I believe you are correct that it is your brake booster.

Check out this link on the operation of brake boosters, might help your troubleshooting:
http://auto.howstuffworks.com/power-brake2.htm

This & the next few diagrams show how it works, and how easy it is to swap. You can use a booster as new as '96 from a junkyard F150/Bronco.

I had the same problem on my old 1980 4x4. The new brake booster didn't cost too much and was easy to replace.

Booster replaced...problem solved. Thanks