If he took it apart then sure, but you can't tell that by looking or testing while it is leaking at the lines. The best advice I can give you is this: START by fixing the leak... this should fix it since it seems it was driving ok before the leak right? If you still have hesitation or problems shifting, then change the fluid, gasket and filter (pretty easy to do just RTFM.) This will cost around $35 for everything if you DIY. If you still have issues, then maybe your tranny is blown - then again, have you looked at the transfer case? Don't give up, I've seen people pay lots of $$$$ only to have the same problem re-surface. If you go to a mechanic, the WORST thing you can do is tell them what is wrong.... let them diagnose and troubleshoot the issue. EXAMPLE: You're vehicle is clanking and driving like crap whenever you turn or accelerate and you know your shocks are blown - so you take it to an honest mechanic and say you need shocks - he replaces them along with new bushings - what if you told him what the vehicle is doing and he finds your shocks are good and only need new bushings???? Think about it.
WARNING: Lo barato sale caro (Cheap things often lead to more expense)