[Petah78]

Car hit 129mph at 8300rpm on 5th gear ???

I think this is the nail in the coffin regardless of what oil or filter was used. Looking at the gear ratio chart posted, not saying this is what happened, it's probable that you are at the top of 5th and going to grab 6th but money shifted into 4th instead. I wonder if there is a delay in the ECU registering gear selection hence the gear read out was 5th instead.

Rather than lawyering up, i will request to review the "black box" data that was retrieved and challenge that. However, i feel this is a extremely slim chance.