So I was driving my GT yesterday, and a couple of times it made a wierd grinding type noise that stopped after a second.. so I examine it after I finish that tank of fuel. Turns out that in the right axle assembly, the o-ring was gone from the stub axle and the one in the outdrive had worked about halfway out, so the dogbone slipping out of the stub axle and spinning. Seems strange, since the truck only has about 3/4 gallon through it. Is that something that just happens with dogbones?

Anyway, it made me consider upgrading to CVDs. So:
What advantages/disadvantages do CVDs have over dogbones?
How do they compare in terms of reliability (ie parts falling out like that..)?
In terms of life before needing maintenance/rebuilding?