i truly don't really know... i just sell parts ... i barely work on my own car... well i do my own oil changes sometimes... i would assume that if you have the tools and are mechanically inclined that it isn't that hard... but i could be wrong...
Yes. Leaking axle seals are very common. However, what also is common on front differentials are the "side differential bearings" failing. When these begin to fail the metal particals have a grinding effect on the seals.
GM has had this issue on all AWD SUVs and not limited to our Cadillacs.
I had my front diff done by someone who said they did them all the time. I let him do the repair and he only replaced the diff side bearings. I asked him how the other bearings looked and his reply was "fine." Needlesstosay, the pinion bearings are now bad and I am sure the axle bearings are bad as well. NOTE** If you are going to do it...do it right and have all bearings replaced and have the axles inspected for wear. You can rebuild the entire front diff, including new axles for around $1,000.
I spent $500 on the first repair I know that I will do it properly the next time to prevent doing it again.