All of 'em really, some you cant see to squirt. Having said that if you remove the plastic ' plugs' in the rear carpet trim to expose the bolts that go through body welded brackets with captive nuts, you could squirt all around the heads and hope some will find it's way down the threads. IIRC, 3 out of 5 snapped, + the other 2 bolt on brackets, as said before. There should be 2 metal straps supporting the bottom of the bumper, bolted to the rear chassis x member. My bolts snapped, and straps rotten, so carefully drilled out, but in doing so it was difficult to drill upside down with restricted space, and I goosed the threads big time.
I drilled these out bigger to accommodate riv nut type fixings with new larger bolts to suit, with new straps I made.
There is a large piece of polystyrene between bumper and rear x member as a cushion/ shock pad, that restricts room too, for wiring, and a further bolt with a plastic cap, holding the rear door stay that needs undoing. The side clips popped apart without too much trouble, just awkward.
That came out easy, woohoo !
The factory fitted sensors are right angled, because of restricted room.
Make sure Mr T is open in lockdown, before you start. The last lockdown came after I ordered my brackets, they came in and my local parts guy there rang and said come and get them ASAP, were closing.
He very kindly arranged to leave them in the grit bin, as everyone was gone when I got there.
Apart from those I had everything else, so I was lucky. Good luck with it.