They replaced the seals when they replaced the Brake Rotors, there was no leak prior to that. The oil level was pretty close to the filling hole and the vent was defenitly not plugged, I checked it twice and the shop checked it too.
The seals installed where SKF 34384, then National 370047A, but there is no information anywhere that these are an interchange for the original W20HH100 or W8000176.
The SKF 35000 look much more like the W20HH100.
As for dimensions, Spicer does not provide any dimension for the W20HH100 or the W8000176. So it is hard to say if the replacements where adequate to start with.
SKF 35000 : http://www.rockauto.com/fr/moreinfo.php?pk=1837330&jsn=8
W8000176 or W20HH100: http://www.shop.classarvrepairs.com/Workhorse-Rear-Wheel-Seal-Assembly-W8000276-W8000276.htm
http://www.ebay.com/itm/Spicer-oil-seal-W8000276-W20HH100-/182560432443?hash=item2a8173213b:g:BzsAAOSwTuJYnI~w&vxp=mtr
At this web site, they list the tools to install the seals and CR35000 is on the same line as W20HH100.
http://www.manualsdir.com/manuals/258975/spicer-drive-axles-illustrated-parts-list-axle-shafts-wheel-end-parts.html?page=20