I'd like to see the oil (after) he changes it in your presence, if you're that interested (and) he's that anxious to sell, it might be worth it. At 15,000 miles, there isn't much maintenance to do other than maybe run the valves and change the air filter right? Buying a bike with those miles on it, you'd have that stuff checked anyway. May be a good deal, with only condensation on the sight glass, helped by being down a quart or so. Why it was down is a mystery though, having 27,000 on my 06 and never having to add oil. Good luck!