Nothing really odd about it, at the age of your vehicle, there is alot of miles on the actuators and all the linkages. There are, literally, about a dozen mechanical joints in the total linkage of central locking doors. Everyone of those joints gets a little play in it, and cumulatively, the stroke of the actuator is no longer enuf to fully operate the mechanism.
The actuators are mounted to plates, each of which has 4 screws holding it to the door frame. The plate holes are sloted, to allow adjustment of the actuator. It will require you to remove each door panel to gain access, loosen the four screws, and mover the actuator AWAY from the linkages, then tighten the four screws.
When you've done the first one, you'll say screw it, and go back to using the key. Or better yet, do like I do, Don't bother locking it. Oh, I forgot, you have 4 times the number of stolen cars per registered drivers than we do. Personally, I don't leave anything in the car worth more than the cost of a single piece of glass replacement. I would, however, like to have