My kids drove my 84 300D (210K) the other day and reported this: with the tank 3/4 full, the gauge needle started dropping and fuel was spewing out of the underside rear near the vent line. They parked it, and the next day when I got there, it started fine and the needle was registering 3/4 tank again, though there was a lot of diesel fuel on the ground.
Any ideas about what could cause both the guage problem and venting? Thanks.

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CH