If you received money back and it cost a grand, that is more than fair. If it's never been dropped, that means no parts to buy. If it comes down to 2 injectors, there is that "I bought it knowing 'as is' and I took the chance I'm going to have to put in whatever it take$." Of course you could have bought a turn key bike and rode off happily ever after. Flip it wise, you made out, don't worry, the PO is off the hook, IMO.
I've heard horror stories about jump starting bikes. You'll probably need a charger for the battery once winter kicks in. You are not trying to start it, you are trying to diagnose it. That spray at the injectors is the 2nd look see. The first thing to see is if the battery is salvageable with the purchase of a smart charger.
Part list:
1. New air cleaner.
2. 4 new sparkplugs.
3. Oil filter.
4. 4qts of oil.
5. Battery charger.
6. Battery (only the smart charger's red light knows for sure)
7. One dry paper towel.
I didn't add injector cleaner. Thought a little more about it. If that paper towel finds the leak, I'd replace it. Then you wouldn't have to worry about the crankcase filling. Figured it leaked when the PO had it, and that was running before he parked it?