Aye Mark,
Common problem.

It goes with the 'fashionable' shorty front mudgaurd and vulnerable position of the coil and plug.
I've eased, but not totally cured the problem by fitting a cheap universal mudflap to the front mudguard, extending it by about 80mm, maybe 100mm.
Cleaning all the electrics, installing a new NGK spark plug cap and using ACF50 on all the wiring under the front of the tank.
Finally, installing a small plastic deflector (ice cream tub) behind the oil cooler, extending down between the front frame tubes and held on by cable ties. Just to keep the spray in the updraft from the front wheel from blowing directly onto the plug area. Don't make this too big, or else you reduce the airflow to cool this part of the head. Same idea as used to be used by Rickman on their scrambles bikes.
Despite all this, I have on occasion, still to resort to the WD40 or ACF50!

Bit dodgy in the outside lane at 70 - 80mph!!!!!!!!!!

My regards, Bill.