I was about to suggest posting on NPORA since not many of us here own WD21s (most of us here have 1996-2004 R50 Pathfinders), but I see you have already have
Sorry that I'm of no help otherwise, but welcome to NICO!
One thing you should probably tell to your customer: if the vehicle has an automatic transmission, the stock cooler is prone to clogging; as a result, many WD21 owners bypass the stock cooler and install an auxiliary transmission cooler. If the vehicle has a manual transmission, there is a TSB for 4WD 1986.5-1995 Pathfinders stating that the transmission must be overfilled; read
here.