On the oil leak, check the filter mount, often a source of leaks. As to the dipstick level, It's actually due to the dipstick seal doing a good job. Dipstick tube bottom is below the oil level normally so with No air leak in or out, when the engine cools there is a vacuum in the tube above the oil level. Oil rises into the tube.
The crankcase breather does not vent air into the crankcase, only pressure out.