[Argess]

Patrick; I think that wrench was intended for the left rear top bolt, not the front.

One way that works for me when I only have one stubborn bolt is to remove all the others, and then twist the part you want to come off CCW.

In this case one would probably have to remove the adjacent primary pipe and the lower bolt of the pipe in question. Then rotate the pipe to loosen the bolt. Once it starts to turn, an open wrench should work.