What's the reasoning behind thinning the oil/atf down with mineral spirts?
I've found that a drop of oil or ATF on the roller seems to wick in perfectly fine. If my chain is dirty or I've neglected it, I'll pull it off and clean it separately in mineral spirits.
I think I will try some gear oil on my chain next time though, I was intrigued by it's tenacious nature when I was using it at work. Brackish road spray seems to clean off the chains pretty well. I've since installed a mudflap that barely clears the ground so that's already saved me a cleaning this week!
I still haven't got around to building my chaincase though, but that'll solve all my rain and slush issues for good.