Hi all, stripping down my 1989 NC30 for major clean and service etc and found oil in the bottom of the air filter box. Is this anything to be worried about and would it have anything to do with the air filter being covered in mould. Couldn't believe how mouldy it was under the tank and in the filter. I am surprised it ran at all, although it did run like a bag of shi#*e.
Any help muchly appreciated.

some is normal, the crankcase vents into the airbox, overtime oil can build up

Just changed my air filter on an 89 and had a little bit of oil in there, have had this on other bikes too, so might be normal

This is normal as the crank case vents into the air box, you can buy a k&n crank case filter which fits onto the vent that the pipe is attached to, just remove the small pipe that goes to the air box & block up the air box side with some silicone. I done this as I run the hrc carb & air box set up & didn't want oil in it.

Ok thanks, panic over then. If it's normal due to crank case breather I'm happy. I will just clear it when I take carbs off for cleaning. Thanks again.