Hmmm... eBay... if they're people with a reputation to maintain, they should replace it free of charge, other than your paying for s/h both ways... which could prove more expensive that buying a nw one yourself...
OR
they could claim it was damged in the mail, but that would be >THEIR< ault because the packaing wasn't up to the required standards.
OR
they could claim you aren't good with oold and damagd it youself - I don't think so.
As for the oil change... drain the oil, open the filter housing, let the filter drip all the oil it can (i.e. through a strainer ) and allow the gas to dry naturally.
IF after a few days it only smells like oil, you should be OK.
IF it still smells like gas, then iscard it.