The rear seal will be above the oil level so I wouldn't expect it to leak when parked, unless the oil is draining out of the bell housing. Just make sure your analysis of where the oil is actually coming from is correct, remember windage across the engine can blow oil down the engine is some instances.
I would check the breather, before you start dissembling things.
1) Are blow by gases execessive? i.e. do you have a ring or valve stem seal problem.
2) Is the breather free and working, i.e. is there only a little gas coming out of the breather, but then what may appear to be more when you open the oil filler cap? You might need to ingratiate yourself to your neighbours and give it a rev up.