We use this stuff, it even gets oil based paint off. The lanolin will make your hands , girlfriend touchable again.
Joes Kleen Products
As far as what is causing it, I don't know. You might try wrapping some tape around the handles where you will be holding it. If your hands get dirty there, then its time to look at the belts OR the engine seeping oil. Maybe even might be a dry bearing grit flying back on you.