The drivers side back (sliding) door won’t open. Cycling the lock, by switch or hand doesn’t help. We traced the (working)mechanism down to near the latch where it disappears behing a sheet metal shield. Two garages have given up on this. Anybody…?
I would remove the seats and see if I could remove the inner panel. I would think that this would have been tried by the mechanics that you employed, so it’s probably not viable. The facia trim between the drivers door and sliding door may yield some type of access to the latching end of the mechanism.
You might want to try a body shop rather than a general purpose shop.
Perhaps I did not make myself clear. We did remove the panel and so did they. The linkage from the door handle goes down to where the actual latch (seen on the other door) connects to the body of the car. The last thing between the rod to the actual connecting mechanism and the body itself is a sheet metal shield in the door itself the rod moves back and forth but the catch does not release the door. The only way to get to that would be to torch it. I was hoping that someone had encountered this before. And, please don’t bother to tell me to take it to a dealer. Instead, just say “STICK 'EM UP!” 
Perhaps I did not make myself clear
You absolutely didn’t make yourself clear. LOL!
You’re as far as anyone practically can go. You’ll need someone who can “get it”. That is, there is no bona fide technique that could be described or written out.
Another resource may be a shop that replaces auto glass and/or power window motors–they’ve probably taken things like this apart.
Thanks to all. My niece, who is some kind of mechanical genius, looked at it and gave up, too. That was really the last nail in the coffin for any hope. I thought there might be one last chance of one of those hidden release secrets - like the little hole on your DVD drive that can open it with just an un-bent paper clip. Wishfull thinking, I reckon. I’ll try a body shop.