Man, honestly? I would be very hesitant to use any drum that's contained anything hazardous/toxic. Heat has the potential to release carcinogens only to be absorbed into your food. Maybe I'm a bit too paranoid, but I wouldn't take any chances with food that my family and friends will be eating. I found a fairly new (date stamped 1 year old from the time of purchase), but once-used unlined drum that contained food-grade coconut oil. That's another thing, if you aren't already aware, I'd find one that's unlined.
As far as the lid goes, mine came with a solid lid (no valve opening) and a locking ring. I scraped out the sealant from the inside of the lid and replaced it with felt gasket. Some smoke comes through, but with my locking ring tightened with a wing nut, it's leak proof. My lid appears to be in completely perfect condition, but the leaks would lead you to believe otherwise, so even an unwarped lid will leak just a bit. I've seen some people weld the ring to the lid and use the bolt hole openings on the ring to use as a hinge mount attached to the backside of their drum, so that they can just swing the lid open komado grill style.
I live close to a drum recycling company and my drum was a whopping $25 and I had the choice between 50+ unlined, coconut oil drums. I chose the one with the least amount of rust inside. It took me not even 30 minutes to wire wheel the inside to perfect condition. If you have to, I'd spend the cash on a brand new unlined drum before I bought a used motor oil drum. I know that defeats the idea of a cheap smoker, but non-toxic food justifies the costs.