cc7y+@andrew.cmu.edu and several others have written:
:  engine compartment.  Seems I'd pared on a slight sidehill (nothing
:  big, just the slant of the street) with a full tank, and the gas had
:  gone right up the fuel fill line and leaked a little...  

The Gerbil (1966) has an overflow tube, which leads from just inside
the gas cap down, and ends just below the battery deck.  It's
positioned such that any overflow misses the engine compartment and
lands on the lower rim of the right-rear tire.  The former seems like
a feature, I'm not quite sure about the latter.

The side-effect of this arrangement is that parking just after
filling the tank such that the fuel-filler side is lower than the
other side results in a puddle of gasoline around the right-rear tire,
and a concomittant strong gasoline smell.

A possibly-related situation is that on warm days, when the tank heats
up and pressurizes its contents, significant vapours are released
through the overflow tube.  This produces a gasoline odor in and
around the engine compartment.  It's great for inducing paranoia about
explosions, particularly after reading this list for a while.

In any case, the questions are:

- Is this a special modification somebody made, or is this standard
  equipment?
- Assuming standard equipment, did they stop putting them in (say, in
  1968, just as a guess)?  It seems like most of the gas-smell
  complaints come from those with later models.

	Dworkin