Fully agree with Tony.
The petcock probably pulls fuel from two ports/locations. The main feed/port is probably plugged with debris that could block fuel delivery at times (hence the lean condition). The reserve isn't affected yet. Note, (not sure if you know this but...) if you leave your bike on reserve from when you fill up, it will run for the whole tank...200 miles or so. That's why you were able to run on reserve for so long.
Pull the petcock and clean it, or get your dealer to pull it. Tony mentioned potential paint flaking off in the tank. If this is happening now, get the tank repaired/replaced by the dealer.
