Ok,

Does anyone know how to replace the front inboard nut that is
inside the crossbar on a Hobie 18 (1985). This nut is what the bolt that attaches the crossbar to the hull screws into.
right next to the hole there are two rivets, which obviously hold this nut in place, but how do I replace the nut?? Do I have to remove the right front corner casting on the crossbar?, and if so, how do I take that off? I don't see any rivets or bolts holding that in.

Any wisdom would be greatly appreciated