Mine leaks a little but not that bad...it must be bent like you said. I'd think the foil, athough not real attractive is likely going to be your best bet as you can shape the foil to fit real good.
The other thing I would do is maybe mark the lid and the bottom so you get the lid on the same each time. This way you'll at least be able to know that you have consistent air flow for lower, slower cooks and may mean you have to close the top damper a bit more than if the lid was tighter.
I have to do the same on my UDS so I get consistent air flow.
2004 Weber Performer GREEN
Orange Super-Duper Fast
Taylor Made 9deg. R7TP w/S-Fujikura 6
Rescued 2002 Weber Genesis Silver B Gasser
SJG Tamale Pot Mini Smoker (SJG was a rescue)
18" Gold (rescue) SJS (rescue)
and a Pyro FIL