Mine does the same thing on my 94. It comes from using heavy key rings with a bunch of keys/keyrings on them. The weight of the keys messes with the tumblers inside the lock and makes it hard to release and turn. Once that happens, you have to jiggle the key a little and sometimes move the bars to release pressure off of the lock to get it to release and turn inside the lock usually both at the same time. The only fix that I know if is eventual replacement of the lock. If anyone else knows of another way, please chime in. Hope this helps.
Treat every stressful situation like a dog. If you can't eat it or play with it, pee on it and walk away.