[myk1323]

Trying to find  either a firm/solid material, or a 'glue' that readily dissolves in gasoline but not at all in diesel fuel. In experiments styrofoam seems to come the closest, but it does end up dissolving in diesel fuel. Thank you.

[Enthalpy]

Diesel oil's composition is very near to gasoline, just with longer molecules. I'm not sure any compound soluble in gasoline would not dissolve at all in Diesel oil.

Can you accept a limited selectivity, as you have already found polystyrene? Or change one of the solvents, say replace gasoline with one that contains heteroatoms like oxygen, nitrogen...?