After my mechanic repaired rusted fuel lines on my smooth running '86 420, he crossed the supply and return lines. We tried starting it several times before we realized the lines were crossed. After correcting the lines it started up but has bad misfire. It ran fine before. He vacuam tested the fuel regulator and it seems stuck. Also checked output at fuel distributor...only getting fuel at 4 lines. The other 4 minimal output with rust and dirt. Would having the supply/return lines crossed and trying to start engine damage the regulator or fuel distributor? Should we try disassembly and cleaning?