Rear door lock inoperative

The rear door electric lock stopped working reliably a long time ago and I would always need to use the key to open it since it remained locked all the time. Now it won't lock when I rotate the knob to the left. I hear it click but doesn't lock. Anyone experience this?

you are having trouble getting it to lock? Mine problem is the opposite it is always locked, can hear power door lock working, but does not seem to unlock, so have to use key. Door lock cylinder was seized, so was replaced, still no function with power door lock. Changing the cylinder not all that bad to change, about $100 for parts, plus having to get it keyed for your vehicle at a locksmiths. ( Local GM dealer insisted didn't have to do that, but couldn't figure out why why door would not function after they replaced cylinder) You will need 2 people to hold door trim as you remove the large panel- not heavy just unwieldy.
Jeff

The lock started working again. Yay, I don't have to tear it apart. I love it when it fixes itself.

Long long time ago, I pulled off the inside plastic mat to install a pair of 6x9 speakers with an extra amplifier (the holes were already cut out at the bottom of the metal sheet: just had to cut out the plastic and add a pair of grilles ) in addition to the original 3 or 4 in. round speakers..that I kept as tweeters by adding a series condenser on each. At same time, I sprayed all latch components with 4w40. No idea what role it may have played, but electric or manual, it still works A1.

The lock was rather rusty but the electrical component was clean and functioning. I sprayed it all down with Rust Free rustproofing spray and it works again. Thanks for the simple suggestion.