2007 SUV:

Sometimes the rear right door will lock with keyfob or driver door master switch, and other times will not.

You can see it trying to lock and unlock as there is a tiny bit of movement.

All other doors lock and unlock function normally with key fob and driver door rocker switch.

I can manually lock and unlock with door switch slider on that problem door.

Anyone have a idea what is wrong? Guessing some worn mechanism or binding linkage.

 

Could be either of what you said or the actuator itself is just getting worn out. I know one thing - many many times I've seen where someone, thinking that they were helping, has added some of the wrong type of grease to the plastic bar guides that the metal rods slide in and over time that grease had become more of an adhesive than a lubricant. Usually some sort of white lithium grease but I've seen black greases get that way too.

Personally, I'd pull the panel, check things over, clean and lube things and see how it goes. Probably just leave the panel off until you know it is fixed for sure.

 

Thanks for that info MixManSC! I will have to pull the door panel and see what is behind it.

Anyone pull off the door panel on this vehicle? I have not.
Not sure what kind of clips hold it on? I really do not want to break old brittle plastic.

 

These are the clips you will need because yes some always break and have some super glue or epoxy ready other things may break also. Since it will be the actuator 98% of the time. Either have it ready or be ready to wait for the replacement so you don't have to pull this panel twice.

 

@Sam! Thanks so much for the photo (which has the GM part number on it). Much appreciate it.
Now that I see what these look like, I can see you just pry the door panel out with a plastic pry stick. Should not be too hard.