We've replaced coil packs, wires, plugs.... vehicle idles beautifully, runs great, accelerates nicely. There is no sign of oil/water mixing and no other symptoms, but we continue to get a Random Misfire (P0300) code. What gives?

check fuel pressure and sniff the vacuum line for fuel on the fuel pressure reg.

which engine?

Ah, just discovered it'* losing coolant....therefore, I've got a bad intake gasket somewhere. But still engine is running fine (for now).