Am I seeing the pu tures right? The contact area on the piston is on the dirty side?

 

How does the wear look under the piston (connection to the rod)?

 

From underneath the piston is like new identical to the others.

 

Did you get your rod checked?

 

What about the oil squirter not cooling the piston properly? Maybe its clogged...

 

The rods were checked and they are Ok and so is the oil squirters.
It's a mystery......
I even checked before dismanteling the engine the oil pressure:
@ idle 0.8 bar
@ 3000 revs 3.7 ~3.9 bars

 

You may not be able to notice an oil pressure difference with a clogged squirter or bolt. I think the spring rate in the bolt is around 45psi. Did the car have a turbo failure before? Maybe something got into the cylinder between the piston and wall causing them to touch.