All of the door mechanisums were cleaned and re-lubed about 6 months ago. Nothing is sticking as far as I can tell.

Sounds like an issue I had 30 yrs ago.  Doused the mechanism with silicone and a lever released and has not stuck since then. 

Just fyi...Tom is/was(?) a member here, and has many tech articles available for these cars. 

Maybe he will chime in on this thread.

Many years ago I had a similar issue with my '78. I had to go through the passenger door to open the driver's door from the inside. A person who owned a body shop recommended trying a product called Free All and spraying in into the door latch and lock cylinder. I had already tried WD40 so I figured why not. It took quite a while to work but I was eventually able to get the latch and door working again. No problem since.

That said, my lock cylinders froze up a few months ago. I thought I was going to have to take the door panels off and maybe wind up replacing the lock cylinders since the Free All wasn't working this time. Before I got into all that I saw an ad on TV for Superzilla penetrant that said it could free up almost anything including frozen locks. I found a product called WD40 Specialist Penetrant that sounded similar, so I bought it. After spraying it in the lock cylinders I was able to turn the key in them within 10 minutes! Unbelievable. I highly recommend this product to anyone having similar issues. It works.

Thanks for the recommendations. In my case the locks & latch had just been cleaned and lubed a few months ago. The latch itself was just in the "locked" position even though the lock levers inside & out were in the "unlocked" position.

Crazy.