I recently bought a '03 Ninja 500R. While my buddy and I were riding today, we rolled to a stop and realized, the under body fairings were leaking oil pretty bad. We go back to his house and realize its the over flow tube from the airbox and somehow oil is getting into the airbox and going through the filter. Now let me remind you that, I bought this bike this week, and today was the first time I have actually got to buy it. The previous owner had it sitting for a year and a half. I am wondering whats going on? It could either be an over fill of oil or even a nest that a rodent had built in one of the airways pushing the oil out through the carbs. I dont know. Need some help, the nice weather is almost here. Thanks!

 

It sounds like the crankcase is overfilled with oil.
To make sure you've got the correct oil level, hold the bike level and squat down to the bike's right. You'll see a little round window below the right crankcase cover. With the bike level (not on the sidestand) the oil level should fall between the upper and lower sightings.
I've met a few riders who think the oil level should fall between those two lines with the bike on the sidestand, which is tragically incorrect.

There might still be a little residual oil in your airbox and accompanying hoses after you get the oil level correct. You can either disassemble and clean everything, or let it get gradually ingested by your intake, which is no catastrophe as long as it's not excessive.

Good luck and let us know how it goes.
Peace!
-Chris in C'bad

 

^+1
An overfill is the most common issue in regards to puking oil into the airbox.