<<Here's my take: I think there is still part of the tensioner that screws into the timing case, you have just the "outside" part (plus the shiny part).
>>

I think G is correct , as Mark sent me a pic of the tensioner hole and there is a sleeve in there that the piston rod [ shiny part] slides in to. That would be where a circlip would ratchet..
The ones I have seen have a hollow , threaded nut that holds this sleeve and plunger in, but this does not ... so, I have no idea what holds it there [ if not just encapsulation from the cap]..
Anyway , that is where to look and check if the circlip was ever seen by anyone.......

Eeh Hah!
 

Thanks to everyone who so persistently steered the diagnosis toward the timing chain tensioner.

I just went to the mechanic, and indeed he was putting the chrome/grey tip onto the chain tensioner body by compressing the clip and installing it from THE CHAIN side, meaning it was fully extended with no chance of sliding into the inner tensioner body to reduce tension because of the ratcheting design.

We pulled the chome/grey tip out, installed the inner body to the block, inserted the chome/grey tip with just one click, then installed the spring and outer cap.

Hand turning the crank revealed reduced tension.

I think we've got it ( hopefully ) , thanks to Arthur, Gilly, M.B. Doc, Paul and all who took the time to review. This is an awesome resource forum!

I'll post again once I've got the car with some run out time to insure all is well.

Mark