TriggerFish said:
Going in from underneath/through the arch won't gain you access - there is a solid inner arch. You can see here how there's a folded lip on the inner arch of the car so you can't access via the wheel arch: https://z4-forum.com/forum/viewtopic.php?p=2127212#p2127212
If you remove the rear light, there is good access to the inner wing that way. You can shine a torch in to see what's going on in there. That'd be my approach.
I just popped to check as I don't have my arch liners fitted - there is actually a gap between that folded lip on the chassis and the outer wing/arch. I assumed that the arch nestled up against the lip on the chassis. My apologies!
However... if that gap would offer a PDR tool enough leverage is a different matter - but it is a gap. I'd probably still try via the rear light first, as it's easier to remove than the arch liner, and offers better visibility of the work area.