On my canopy side vent, one of the brackets broke where it meets the
rectangular vent. I tried super glue, epoxy, plexi sealant from Lowe's...no
luck.

Fixed it beautifully using Weld-On glue, available from
http://www.stewmac.com/shop/Glues,_a...t.html#details

Glue is $5.10 plus $8.25 shipping.