It happened over 40 years ago now and I've looked over lots and lots off footage (as you know from my youtube videos) I know there is still footage from the stages and service that has yet to be seen.
In my opinion, it was either driver error or simply the throttle jammed and Henri went off. I...
The Delta S4's didn't have Nistros in the roll bar. I think people mix up the rumours from the 1988 Sanremo where Lancia were seen to be changing the fire extinguisher's at service. Which lead to rumours they were using them to hold NOS.