I use a cheap chain lube from princess auto. It’s more on the liquid side. Where do you think the oil leak could be from? There’s never a puddle of oil on the ground after riding so I’m hoping it’s not leaking oil
Use some brake cleaner to clean the area then dust it with some flour or baby powder. If it's leaking the source area will become apparent. But if you're not seeing a leakage under the bike, I'd reckon it's just oil from a past filter change and grease from chain lube.
Clean it all up, clean the chain, and go for a ride or 3. See if the goo returns. If you are using an o-ring chain don’t even worry about lubing the chain for a few rides. Even if it’s a plain roller you won’t do any damage to the chain in 25-50 miles.
That is a notoriously grimy area of every motorcycle, especially one where a lot of chain lube is used.
All of my motorcycles run x-ring chains. I never ever lube them, but I do clean them from time to time. The only lube I would use on a chain is heavy weight gear oil. I brush it on like I’m painting the chain, on the inside surface only.