Hi, recently had to change my throttle cable after it was installed incorrectly by the PO and crimped itself at full throttle mid corner...but that's another story, basically as I removed the airbox I found a fair old amount of oil in there, mostly misted but some pooling as well. As far as my understanding goes, this is usually a sign that the piston rings are on their way out or the oil has been overfilled and forced its way past. Is this fairly common on these bikes or should I be considering a leak down test and some serious overhauling of the engine?? Is it true you have to split the case to put new piston rings in on the nc30's??

First and easiest thing to check is your oil level, if that's OK then I'd give the airbox a good clean out and check to see if you can replicate the issue. If so then look into the not serious options (ie piston rings etc). [GRINNING FACE WITH SMILING EYES]

the oil breather is routerd through the airbox some some oil condensation is normal, if it hasnt been cleaned ina long time / overfilled too will add to it.

clean it all out, make sure your oil level is ok and see how it goes.

It's had 20 odd years to accumulate in there so probably all is ok. Give it a clean and try it for a while, I bet after a 1000 miles it's still clean!