Hey Johny,
I am not familiar with the axle on 3Bs, but the holes you are describing are the breathers on the top of my 3A axle tube. (Dana 41)
As described by others, they can and will get clogged, and if they do, the axle lube will push through the seals and gaskets on the axle. If you go 'Muddin', best to check them and clean them out if needed.
There are some discussion on posting pictures on the site. Hosting sites like Photobucket (free) are the only consistant way to get the photos on the Tech page. Look at the Web site feed back page and you will find pretty good instructions.
Tim