[demian5]

Ok, so I bought one for my truck. A 1970 and earlier 10491.

I blew through the back of it, pressure was released (unlike the 10582 I have that i can't blow through since the tank is supposed to have a vent on this model year). I think "awesome, solved!"

Put it on, make some on ramp maneuvers, gas all over side of truck.
Seems to seal, the lock mechanism is a little lazy compared to the old one... lets return it and try another one.
Replacement cap, same thing. Gas all over. Lock mechanism lazy on this one too.

Back to the cap I've had that builds up too much pressure.

I would like to see what the "hole' thing is about for the current cap. Or maybe I try a 72 cap, but that would be the same as the 71 I assume. Maybe I try and pull the pressure mechanisms out of both caps and swap them...

Ill keep trying stuff till I fix it. However, I know this has been solved by somebody.

The funniest thing I have learned about this (don't tell ANYONE) the keys interchange and work between all of the caps. Buy a cap and open your buddies gas cap...