Flash Flanigan faked his deathI find it odd that so little is mentioned about this character. All we know is that he had an accident after a concert presumely the one where he stormed off. What if he got sick of Susan's constant control, faked his death and went into hiding.
Murf the Mechanic is Flash FlaniganIt would explain his obsession with the mystery kids. It would also explain his obsession with the van. Since Flash Flanigan painted the mystery machine, it would be understandable why he wants it back.