Spencer I think you want "distorted thread" M8 lock nuts for the case perimeter. Rather than DIN 985 Nylocks, because the nylon can melt and leave you with no locking. In the later cases the Factory specified such a nut, I haven't checked PET but I'm pretty sure.
Here is what they look like:
Now, the torque settings are useless with this type of a nut, becuase the friction from the locking feature will make the wrench click long before the requisite preload has been obtained. So measure with a stretch gauge -use a conventional DIN 934 plain nut with the same washer, bring to fastener to clamp load until the torque wrench clicks then measure the length between the back of the flange and the head of the stud with a micrometer, then install the lock nut and turn it until the same stretch is achieved.
Or just tighten it with a wrench by hand until it feels tight and call it cool.
