Another option is HySol Epoxy
made by Loctite.
I use it for gluing and bonding and have fixed several tank leaks with it. Lancair builders glue their wings together with it. (wet wing)
Mix, smear onto a clean surface around the rivet and let dry. Touch up paint as necessary.
For larger leaks, "be done with it"
fixes, the guys at Weep No More do excellent work on RV tanks as well as my friends Hollywood and Cheese
at Hotel Whiskey Aviation.