Recently did valve cover gaskets, and there's a small leak in the rear of the passenger side one. Is it ever a problem with the cover itself (crack/warped), and not the gaskets?

If I recall, you are supposed to put a bit of sealer in the corners. I think the FSM shows where. If you did not do that, it might be the cause of the leak.

Randy

FSM sez a thin layer of RTV in the channels on your half moon seals. Set them in place and let them cure up a couple minutes before you put the cover back on.

When I re-did mine(after the head job set), I hit all of the areas where the previous leaks were comming from, and still have a small leak. My Sister had a leak on the passenger side cover show up shortly after the dealer adjusted the valves, so simply following the FSM doesn't always do the trick. When I do them again I am going to hit the entire outer edge w/FIPG.

A crack could be the cause, but unlikely unless you over tightened a bolt when putting them back on. An inch pound torque wrench should be used over a Ft lb or hand tightening w/1/4" drive and not a lot of force.

I had the same problem, assuming we are talking about a 3vze. Turned out the gaskets I purchased were not thick enough. Got the gaskets from toyota and they were noticible softer and thicker....problem solved.