Hey Tom we are generally diligent with the cleaning of the air filter but on that occasion it had been about 2-3 weeks without a good clean with some desert sand etc. but the filter did not look overly bad when cleaned. Fitted properly. Oil looked black with a low viscosity. Serviced every 5000-5500 km and needs the 40 000 km service now.
I believe the oil leak occurred when I over filled the oil on the first service of the trip. But only about 4000 km ago she started sweating oil from the gasket around the crank case cover (front). Due to not having the correct seals to remove the crank case cover I used gasket maker to seal the area, with 100% success so far. No leak.
The small ping on acceleration has been happening for +\-1000 km but I thought it could be a carbon build up.