Saddle Tanks Overflowing After Fueling

[ahoke]

Hi all,

Picked up a '72 C20 Custom Camper this summer with the two additional travel tanks added on either side of the bed. When I purchased the truck, the owner said he didn't use the cab tank because it smelled like gas when he did.
Essentially once I fill up, I'll drive it and park it and some time later one saddle tank or the other will overflow, leaving a slight puddle of gas on the ground. When parking I'll look underneath and there will be no sign of leaking but then coming out of the grocery store, for example, there will be the leak 20 mins later. Anyone have any similar issue? Curious if I just need to replace the 4 way brass tank selector valve or if it's more than that. Also I never fill the cab tank since the previous owner mentioned the fume issue. Initially I thought maybe the valve was bad and the fuel left in the cab tank was slipping back into the saddle tanks due to gravity and maybe it takes that long for the fuel to accumulate into the tank that I'm using.

If y'all suggest trying a new valve any suggestions on where to buy one? Seems like a marine part. I imagine it'll need to be 3/8 inch since it's a 350 sbc?