i never assume that someone has done the work even if it has receipts, its easy to knock up fake papers... same goes with odometer readings - theyre easy to wind back if needed.
when you buy a second hand car, replace and FLUSH OUT every fluid - engine oil, coolant, trans, diff, brakes, power steer. all filters.
i did all of this and still had my gearbox die a year later thru normal use. a $3000 repair due to a $10 clip breaking