My early BAD habit was to reach up and check that the fuel caps were on and tight for Citabiras. I was tall enough then to reach up and give them a twist.

Then one day, on my first trip to Idaho in Oct. 83 I stopped in Windyschmucca for fuel and a break. There was this beautiful young lady doing the fuel work. Still have the photo. She kept asking me about my trip and wanted to go but Momma said no.
In those days she would have been as safe with me as anywhere. Honest.

Any way I do my usual reach up and twist the caps and both were on and tight.
For those that do not know these are "flat" caps with two prongs, no tall handle like I had on the 170. More like a lawn mower or late forties Dodge I once had.

Well... somewhere approaching McDermot I just happened to look over towards the highway, and just happened to notice that the fuel guage was near EMPTY.

To cut the story short: I found that the caps can be put on with one of the tabs NOT underneath where it belongs and still feel tight. So the cap was on with the back third or so in the air creating and excellent vacuum generator.

EVER-AFTER I always made sure I got HIGH enough to verify that the damned caps were not only tight- but FLAT- with both tabs tucked away where they belong.
"Nevermore," Quoth the Raven, "Nevermore."

This thread made me a bit paranoid.

The caps on my Citabria are a bit dented up and their natural, correctly installed position they look wrong. I took them off and flipped them over so I could see how they "sit" with the tabs removed from the equation. I took a good walk around to look at the caps from all angles so I know where the right position is.

Haven't had to lube the seals yet, and they really do go on pretty squarely. I do get up on the wing and dip the tanks and verify caps already but now I'm going to also add the visual inspection of the caps to my overall last lap around the plane before climbing in

So I have the Monarch raised caps on my 195. Their owners have a love/hate Ford/Chevy type relationship with them on the Skywagons forums. Anyway, I recently went camping and landed at a deserted strip and noticed I was missing a cap. I covered the cap with an occlusive dressing for sucking chest wounds. This kept moisture out but the glue is a real pain to get off. Definitely using duct tape if it happens again.

Anyway, I'm pretty certain that the cap was on when I left. I'd say 100% certain, but there is that little bit of doubt in the back of my mind. Occam's razor, and all. But I did fuel up a couple of days before I left (not in a hurry) and preflighted the plane in the hangar where I can clearly see the caps from behind the wing. For those who aren't familiar, the Monarch caps have a plastic screw in type fitting and ratchet, not unlike a modern car gas cap. So the ratchet prevents over-tightening, but if the ratchet is worn, or the gasket is worn, then perhaps it won't tighten enough?
Anyway, when I bought my very expensive replacement cap, I noticed when I tightened the cap down, it was much harder to engage the ratchet and feels much firmer. I also replaced the gasket on the other cap just to be on the safe side.

What I will say about the Monarch caps is that they also have a little flapper inside the filler neck so I lost approximately zero fuel.

I like Barnstormers idea of using Marvel Mystery Oil to lube my cap gaskets. That way if I happen to spill about 3 oz./10 gal of the stuff in the tank during the process, I end up with cleaner exhaust valves, and lubricated stems.