The brief
The E250 was due for its transmission fluid service, Mercedes calls for it at the 60,000 and 120,000 km marks, and the owner wanted it done on time. That's the right call, the fluid does the lubricating, cooling and clutch work in there, and keeping it fresh is what keeps the shifts crisp and the gearbox healthy. This is more than a drain and refill. The service means dropping the pan, replacing the transmission fluid filter with a fresh gasket, refilling with the exact Mercedes-spec fluid, and then setting the level with the gearbox at the right temperature, because it's a fill-to-temperature procedure, not a dipstick. Done right, it's the cheapest insurance there is on an automatic.
The diagnosis
A check confirmed the gearbox was shifting fine, no slipping, no flare, no fault codes, just fluid that had reached its service interval. The pan and filter were due with it. So it was a straight fluid-and-filter service: drop the pan, fit the new filter, refill with the correct fluid, and set the level properly at temperature.
The work
The old transmission fluid was drained, the pan dropped and the transmission fluid filter replaced with a new genuine Mercedes unit and a fresh gasket, the magnets cleaned off. The gearbox was refilled with the exact Mercedes-spec fluid, then brought up to the specified temperature and the level set precisely the way the procedure calls for, with the fill plug torqued to spec, and the adaptations reset so the gearbox relearned on fresh fluid. A road test confirmed clean, crisp shifts through the range with smooth pull-away and no flare.
The outcome
Crisp shifts, smooth pull-away, no flare between gears, and the gearbox running cooler on fresh fluid. The E250 went home with the transmission serviced on schedule. Fluid that's done its interval loses its edge and lets the gearbox run hotter, so changing it, the filter and the gasket and setting the level right is the proactive job that keeps a good gearbox a good gearbox.