First, your drive shaft should be balanced. If you've lost a weight you should take it to a drive line shop and get it repaired. Pinion seals can last for ever or go 10000 miles. I doubt an out of balance shaft will take out a pinion seal. Pinion bearing packing it in can take out a pinion seal . If a pinion brg is gone you will feel "up & down" play on the pinion shaft if you grab it and try to move side to side or up and down.
New drive shaft angles will not nessisarily cause a vibration - increased angles can cause more strain on the u joints and take them out sooner. If the dl angles are sharp enough to cause the u joints to bind you will get a vibration. Seized u joints can also cause a vibration. Wore out u joints will clunk usually - may not notice a vibration. drive shafts out of phase may cause u joint binding ergo a vibration. If you separate a 2 pc shaft and don't re assemble exactly the same you can get a vibration. If you replace the u joints and don't line the yokes up the same you can get a -- yup vibration.
Proper phasing is when all the yokes line up excactly - in a straight line and yokes line proprerly. The "Y" of the yokes need to match directions of pointing. You can get the yoke of one shaft out of phase with the yoke of the other.
Now back to the leaking pinion seal. Tall grass it gets wrapped around the pinion yoke it can work into the seal and take it out. Anything that can get into the lip of the seal can take it out. A little hard to do but not impossible. Mud, dirt, sand etc.
Or the seal can just wear out and leak.
Last edited by Phyer Phyter; 03-22-2012 at 12:03 AM.