Well that can only be said once it's opened up. There might be some bits that are still working but nearing the end of life so it makes sense to replace them since you are in there already.
Also depending on what you want to do, you can ask then to do a full rebuild as in replace everything that can be replaced but that would mean more $$$$ or ask them to replace the broken bits and the ones that look they are at the end of their line or you can say just do enough work so it drives again.
I think in your case seeing the age of car and costs involved I would say go for the middle option
Also many many gear specialists already have a stock of boxes ready to go for example you came in and replaced your transmission. What they then do is repair your old transmission and stock it, so the next time another Pathfinder comes they just replace it with the one they have in stock, send hin on his way and then repair that one and stock it for the next one, so on and so forth. So you might actually end up with someone else's old repaired box.