AS much as I would like to give you a FANTASTIC answer, there really isn't one. Seals can fail for no particular reason. The seal may have just worn out, or it may have gotten a piece of dirt between the seal and the crankshaft. It could have been defective and failed prematurely. There may have been a nick in the crankshaft that cut the seal while it was in use. The more importand thing to consider is when a new seal is installed, you must check the crankshaft to make sure there is no wear or any nicks in the shaft...or... the new seal that you instal bill do the same thing. Make sure that you use a good SEAL installation tool to protect the seal while installing it. This tool is a very thin plastic sleeve that is just every slightly larger than the crankshaft that is slid over the shaft to protect the seal from getting cut by the keyway in the shaft or any other imperfections on the shaft.
If the seal was defective right out of the factory, It could have been caused by not only a defective seal as I had stated before but it can also be caused by a nick in the crankshaft. If this is the problem, the crankshaft will also have to be replaced. This is why I said to take it to a GOOD dealership to have it repaired by a warranty dealer. You do not want to have to do this again very soon. this is why I mentioned all of this in my previous answer.
If it is NOT done at a warranty dealer, they the warranty will not par for this repair or ANY OTHER repair in the future if they don't do it right. The answer does not change. You must have this done professionally to get it done right.
There is always a possibility that there is something pressurizing the crankcase but this is something also that will have to be tested with a pressure test at the dealership.
Sometimes there is no easy answer and especially if it is under warranty.
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