Car Door Locks Won’t Turn

I have a 1998 Mercury Grand Marquise that doesn’t get driven much.

While it does have remote door unlock, since the car doesn’t get driven much, I disconnect the battery.
Hence, I must use the old fashioned key to unlock the door initially.

Last time I drove it I couldn’t get the key to turn. It wouldn’t turn in the driver door, the passenger door nor the trunk.

I eventually jiggled the key enough to get the door unlocked, but this concerned me.

NOTE: the key works fine in the ignition.

A locksmith told me to spray a WD-40 type lubricant in the key hole.

I’ve always heard to use a graphite powder instead of a liquid lubricant.

I also decided to search the brain trust of YouTube.
…and yes, I found someone touting the same solution.

So, I tried it. Unfortunately I didn’t take a video, but it worked like a champ.

I stuck the little straw in the key hole, sprayed.
Put the key in, and presto, works like a champ.
I then did this on the rest of the locks and they all work great now.