Rear Differential Fluid Question

[GTSideSwipe]

Hi, so I have a little bit of a question regarding the rear differential fluid. I just had the rear differential fluid changed about 150 miles ago and I'm having to continue to take it back multiple times because it keeps leaking and they have cleaned and resealed it but no luck. What type of fluid do you guys recommend using? It's a 10 bolt posi 4.10:1 HO52 rear end by what it looks like and I've already check the gear ratios by pushing the vehicle and paying attention to the rear wheel rotation and drive shaft rotation. I am just losing trust with shops because I keep getting half ass work. I already am doing the brakes, oil change, and cosmetic work myself so I'm just going to do all of it.