Oil cap from engine #3. I own an oil cap like this, and this was the first
opportunity I had to take a picture of one (I couldn't get above the wing
I overheard one of the crew telling another visitor about the oil tanks
(presumably in response to a question about the ever-present drips of oil).
Apparently, the B-24 (at least the -A model) has oil tanks built into the wing
structure, as opposed to having a separate tank structure. This increased the
amount of oil leakage. To combat this, the folks who fly Diamond
Lil created a "tank within a tank" to cut down on oil losses.