Tractor Repair: 28 HP Kubota tractor, crankcase breather, correct oil

Question
Why is there pressure build up in the crankcase to the extent it pops the rubber plug out and allows the oil to get over everything?

Answer
Sounds like your crankcase breather is plugged. Or there is to much oil or you have coolant in your crankcase causing the level to be to high. Check the breather and your oil level. That should fix your problem. Make sure you have the correct oil filter also.