It could be something simple/stupid. But, and this is the thing, the reason I don't buy used vehicles almost ever anymore is this - you NEVER know what it went through prior. I don't care what some smarmy dealer says about the history of the bike, they have NO IDEA if it did smokey burnouts constantly or tons of short trips that caused excess moisture and acids to form in the oil, or was lugged constantly, or was started and "warmed up" idling for 10 minutes at a time, or was overheated a few times or ..... When you buy anything used you roll the dice no matter how well it is inspected. Most of the time, you're fine. Sometimes, even just once in a while, you're not.