my 2 cents...
FYi, just so you know, the clutches inside a tracloc unit work similar to most transmission clutches/bands. Basically the fluid lubricates everything, bearings and what not, control heat a bit, and clutches bite better when they are wet. Having changed fluid in the rear end could cause the traclock to stop working from the standpoint that the clutches might be so worn that the friction from the old clutch particles that were suspended in the old fluid was all that held. Now with fluid with very little friction material in the oil, no biting/functioning of the clutchpacks. See it happen in high mileage auto transmissions once a fluid change happens, in for maintance, and then back for a trans rebuild.
Proud Owner of a 1990 Mustang GT 5.0 T-5
Modified by previous owner..Cheezy 5 PSI Powerdyne Supercharger,Lowered approx 2"for now,Fresh Paint, MMR Rear Coilover kit with lakewood 50/50s, MM k member brace, CHE rear strut tower brace, suspension and chasis stiffening started, Rear End in progress..