Well, after walking away from the project and clearing my head for a little while, I saw that I could gain access to the clips from some other angles than I was approaching them initially, and I managed to get the front three loose! The one closest to the firewall - not a chance! So, I doused it in tri-flow, gave it a little tug, and it came free! So, my three-day-long struggle is almost over, as the rest of the jof has gone relatively smoothly so far. I'll do a detailed write-up of my experience with this very challenging job, so maybe it can help someone in the future.

One glitch - I lost one of the clips. It went flying as I yanked it loose, and it's vanished. It's not in the cam area, so I don't think it's in a dangerous spot, but it has definitely disappeared. Unfortunately, it's apparently no longer available as a separate part, but my local dealer is trying to locate one. Film at 11...

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT