The stator coil does not affect your spark unless the battery goes dead. The stator windings are lacquer coated and won't be troubled by oil unless the windings have shorted to themselves. If you are still getting a charge to the battery that goes above 12.7v at around 1700 rpm them it's not the problem.
For weak spark, check the voltage at the ignition coils red/white wires with the key on. Optimally what you want to see is no more than a 0.5v drop compared to battery terminal voltage. If it does have a big voltage drop then suspect, the ignition fuse, handlebar kill switch contacts, mainswitch contacts and all harness connectors on the Red/White ignition circuit.
Guy