I got this really, really cool "no name" lens. But the focus and aperture rings were stiff and un-smooth and i actually needed two arms with much force to focus it. So i got some gun oil and i think i sort of overdid it: putting ~30 drops of the oil for both rings. The rings loosened up but I fear that the oil can get inside the lens and get onto the inner elements.

Can anyone describe how oil and other things can get inside the barrel of the lens and on to the middle elements ?

[Note: the optics on mine seem ok, but i think this is a reasonable concern. I also realize every lens is different. So maybe taking all that into consideration can help.]