I can't seem to keep the water out of my axle bearings causing me to replace them every 4 months. Has anybody else had this problem? What might some solutions be?

 

When you have your axle out, check to make sure that that area on the axle that comes into contact with the seals are smooth. If they are rough they will tear up your seals in a matter of minutes and water will be getting in right away.
If it's roughed up, you would be wise to buy a new axle. That's what I had to do.

 

My axle is smoothe where you mentioned. I think it's coming in from somewhere else maybe further up on the swingarm. Any other suggestions?

 

When you replace your bearings have you had the bearing carrier out? If not, take it out and inspect it. There is no other wat for water to get into your bearings unless the bearing carrier has a crack in it. It is a solid piece of aluminum with the bearings mounted in it and then the seals. No way for water to get into the swingarm and then the carrier unless it's damaged.

 

If you mean when you loosen the bolts to adjust your chain and water runs out, that is normal for a 400ex. The water isn't in your bearings at that point. The water is between the carrier and the swingarm.

The only way for water to get into the axle is through the two seals you mention on each side.