CEL on, random misfire, mechanic suggested plugs and wires. 160K on car, found oil in spark plug tubes so I replaced valve cover gaskets and seals, plugs, wires, cap and rotor. Still CEL comes on P0300. Replaced distributor with Cardone rebuild, Advanced Auto part# 31-49600, still getting P0300- only now instead of having to drive 80 to 100 miles before code comes up, in will come up in less than 30 miles. I still have the core.

Q: What next? I am at a loss.

Thanks in advance (no pun intended)
Chuck