[Milsurplus] "Sealed for Life"

[CL in NC]

I have a lot of milsurp that runs on their dynamotors.  All of them I have disassembled, cleaned and lubricated the bearings of.  But, the DY17 for the ART 13 says no maintenance is needed, the bearings are 'Sealed for Life".  So, in the real world, what is the experiences of you folks that may be running a DY17?  Are they really sealed for life or does the dynamotor give you some indication of condition by noises?  I know the only real way is to pull all the brushes and see how the armature feels when your rotate it,  but maybe there is a tell tale that confirms I have to go to all that trouble. 

Charlie, W4MEC in NC