Random question - are the u-joint bellows a sealed system?

[GMTK]

Out of curiosity - are the u-joint bellows designed so that NO water at all gets in? Specifically, I have a SX-M and am was wondering if they outdrive is designed for no water to get in. Only reason I was thinking about it was because the gimbal bearing calls for the same grease as the trailer bearings which it typically a water-resistant type grease.

 

[further]

Yes sealed. Water is bad for u-joints and gimbal bearing....

 

[GMTK]

Ok, thanks. Learn something new everyday.