Have you tried Ductape???
Jus kidding ........ :)
Johnstone Supply carries a Pan Epoxy Patch kit which consists of a two part goop which is said to seek it's own level in a drain pan.
Possibly you could goop this stuff on the areas which are leaking.
I like the welding idea the best though.
My personal sugestion is to go with a gas shielded SS MIG unit. Or you can have the pan TIG Welded, heli arc.
Wish they made a Dactape loaded with some stick-um which would adhere to most anything.
Tsk, tsk...... maybe in the near future....