All doors locking/unlocking intermittently

My '98 power door locks have worked flawlessly until last week. Occasionally now, when locking with key or rocker switch, they will click, and one or two may go down partially, but won't go all the way down. Sometimes driver, sometimes passenger, sometimes slider... sometimes all. Same thing when unlocking; Occasionally one or more may come up only partially...

I'm sure not all the actuators have gone out all at once; there must be some master vacuum cylinder, hose, or relay that has sprung a leak or contact has gotten corroded.

Any suggestions?

Also, my Haynes manual does not mention the locking system at all. Is there a more comprehensive manual that covers such things as the operation of the door locks in detail?

Any help would be appreciated!

My "Phantom Lock Button Presser" wound up being some luggage bumping the lock button next to the rear door.

Karl.