KY Jelly?

So can anyone give me the good oil on 'the good oil'? Why would such a term describe the provision of good, reliable or latest or inside information?

Goddess, are you sure you're not talking about KY jelly?

Ha ha, no Acme - there are some things a person shouldn't need - but I'm not going there.

You know what I mean (you're just playing hard to get) - give me the facts man, the latest info, etc. etc.