Doors will not Unlock

Hello,

I have a 1990 Toyota Camry DX. Throughout the past year or two, my front passenger door would go through periods of weeks at a time where it could not be unlocked--not with the power lock button and not with a key from the outside. When a key was attempted, it would not turn even a little without great pressure, and I did not want to break the key of course.

The passenger door was recently in that locked state. Last week my driver door momentarily locked up the same way when I inserted the key to unlock it. After a minute it did unlock and function properly, and my dad squirted some WD40-like lubricant into the key hole, which then facilitated key turning--whereas before there would sometimes be notable friction when turning the key, and you could hear it.

Today when I left the house, the driver door would not open for me with the key, but thankfully the front passenger and the back doors did. When I left my father's house, neither of the front doors would open. Note that I do hear the solenoid working. That is, there is the loud lock/unlock sound coming from each door when the power lock button is pressed.

Question #1: What is the problem? Why are the locks working sometimes, and sometimes not? Is this something that can be fixed by accessing the lock mechanism? I've reviewed the Haynes manual, but I don't know what the problem is yet.

*****

Also, a few weeks ago, the inside door handle pretty much popped off one day when I went to open the front driver door. The spring ejected and part of the plastic handle itself snapped off. The remaining portion of the plastic handle still connected to the "Door Opening Control Link" was enough to be able to pull forward (toward the front of the car) in order to release the door for opening. My dad then rigged it back into place to function temporarily as a lever. After this handle snapped, sometimes the door would not close fully--there would be sort of a banging sound when closing the door (rather than a latching or clicking) and the seat belt would not slide back, which is how I knew it wasn't really closed. I would have to swing the door open and pull it shut again a little harder to close it.

Question #2: Was the breaking of the handle likely a result of a problem inside the door that itself needs to be fixed? I was thinking of removing the back door handle, using it to replace the fornt door handle (since my back driver door has recently fallen a bit low when opening, needs to be lifted upward strongly to close, and I never use it anyway), but I don't want to switch it if it is just going to break anyway from some internal problem inside the front driver door. And does this issue have anything to do with the lock "freeze" in my first problem?

Sorry for such a long description. I just want to give you as much info as possible. And I really need this car to last me until I start school again in August. Thank you for your help. :)