AE diffs suck.... they feel gritty quickly and that's because of the thrust bearing. well most of the time anyway. If you build it right, and it's perfect, I'm told most guys still only get 2-3 weeks on a diff. Myself, I run the thing for 2 or 3 months before I even think about touching it... My diff usually feels gritty after 3 runs but will stay the same for 3 months... it doesn't get worse until it just goes. When I get more anal and am more prepared, then I'll slap a new diff in every month. I actually am going to build a complete second transmission and just swap it out for rebuilds / big races etc...