I bought the Basenor mud flaps on Amazon. Like many, I had to deal with the difficulty of one of the bolts being difficult to remove. The passenger side was no problem; the driver's side was hard and I ignorantly torqued it until the internal spot weld holding the nut snapped, and then the bolt was stuck, spinning freely. Thought I'd help others who fell into this trap.
One thing I couldn't figure out was how to get the mud flap on with the nut/bolt. Since installing the mud flap requires the fender liner to be popped back in place, I have no access to hold the nut from spinning while screwing in the bolt. In
RPM's video, they solved this by using a plastic grommet. The grommets that come with the flap are the same size as the Tesla ones in the fender liners are are not a good length to replace the bolt in a secure way. Would welcome suggestions or a solution for this!
I recommend some vice grips like these with narrower tips to get at the nut.
After you follow the instructions to remove the two plastic grommets and the thumbscrew in the fender liner, you can pop the liner off the fender with a flathead screwdriver and look at the problem area.
Once you get a good grip on the nut and some WD40 or liquid wrench, you can get the bolt free of the nut. And here's the nut itself.