Key won't open stiff door locks

[Cal Learner]

1990 GXE. Checked the search feature but didn't find a thread to help me. What is the recommended way of lubing/loosening up the door locks so that the key turns the lock from the outside? The lock mechanism is so stiff that the key often doesn't turn at all, or if it does, it's very stiff. The car has spent most of its life in south Florida, so ice is not the problem here. Suspect it's just age and wear. TIA

[Fezzik]

Try getting some white lithium grease and spray into the keyhole. Sometimes the keyhole can rust or get gummed up.

[Cal Learner]

Thanks Fezzik. I'll do that. Will inserting, removing and jiggling the key inside the lock distribute enough of the grease into the mechanism to loosen it up, or is something else required to get good coverage in there?

[Fezzik]

Nope just put the red straw tip in there and give it a good blast or two. Moving the key in and out and rotating it will help the moving parts get the greese.

[MinisterofDOOM]

It's also possible that your key is to blame, especially if you're using a copy (or even a copy of a copy). I've had problems with my copied keys wearing down over time to the point where they won't operate the doors anymore. If you still have your car's original small number plate (it originally came on a keyring, and is maybe an inch long) the dealer can still cut you a "true" brand new, clean, perfect key from scratch. That may solve your problem. Copying keys over and over again over the years slowly degrades the shape, and eventually you end up with something that doesn't quite work in the tumblers anymore.