What would cause a rear main oil seal to all of a sudden start to leak on a ZD326 with 400hrs? It has been about 60hrs since the last oil change and I make frequent checks on all fluid levels. Today I noticed a wet spot on the garage floor behind the mower and found oil on the frame under the flywheel. Checked the oil level and sure enough it was down a little. It is hard to get a good look in that area, but it appears to be the rear main seal leaking. Any ideas on what could be the cause.