I am replacing my rear crossbar on a 1991 H17 as it has cracked on both ends just inboard of the hulls.

My questions are well, a few about the backup plate 50253001. Its not in my manual or as far I can tell on my boat.

Where does the plate go?
Is it a retrofit item of later years that is backward compatible to older existing rear crossbars?

Cheers for the help

I've got this sorted now. There is a small plate riveted inside of the cross bar. The cracks start at the rivets.