My new-to-me Mini came with the worst dipstick I have ever encountered. I've seen some beauties that made reading the level difficult with clean oil, usually because of shallow hatch marks. Mini's dipstick is engineered to smear the measuring section whenever you remove the dipstick. It looks like an intentional design. The solution is to either modify the original dipstick, to use an elaborate pull it out, wipe it, stick it in, pull it out and wipe till you get dizzy method, or to buy an aftermarket dipstick. That's the one from Cravenspeed in the picture below and it works well. If I had a difficult to read flat dipstick I'd be inclined to drill small holes through the measuring area.