Well my experiences are limited just hearing what others say and the handful of axle services i've done. But I feel like my beliefs are justified since one of the packets of grease I received in a recent GKN boot kit purchase leaked out and got the box all oily. My point is that if the grease got oily, it's likely an economy petroleum grease that can separate pretty easy. Good synthetic greases remain a uniform goop and don't separate. Plus they're just simply better at lubricating long term, just like most synthetic oils.
But this is all probably overkill since it'll take another 20+ years for the axles to wear out? I dunno. Maybe it's my pessimistic view of today's quality in everything. The original axles were built with better boots and better grease and were actually brand new parts. Whereas stuff made today is all about the bottom line, remanufactured and mediocre quality at best. We've seen new steering rack boots split within a few years, new CV boots split within a year, new rocker arms fall apart (follower pad), crappy quality of engine valves, shoddy engine bearing shells, crappy gaskets......... The list goes on. What a shame.
