The brief
The E250 had been leaking transmission fluid from the ATF pan gasket, with the fluid level dropping and the shifts not as clean as they used to be. He brought it in before a minor leak became transmission damage. The ATF pan gasket seals the bottom of the automatic transmission, where the filter sits, and over time it wears down and lets fluid escape. The ATF lubricates and cools the gears and clutches and carries the hydraulic pressure that shifts them, so when the gasket weeps and the level drops, the box runs low and shifts worse, and old, heat-degraded fluid makes it worse still. Ignoring even a minor ATF leak can lead to serious transmission damage, so it gets the leak fixed and the fluid done together.
The diagnosis
On the lift the leak traced to the transmission pan gasket and the filter seal, both weeping, with the rest of the transmission housing dry. The fluid that came out was dark and tired, well past its best, so it was getting a full change while the pan was off. So the call was the full ATF set, drop the pan, new filter, new pan gasket, fresh fluid to the correct spec and level, rather than just topping it up onto a leak.
The work
The transmission pan was dropped, the old fluid drained, and the old filter and gasket removed. The pan and the magnets were cleaned, a new genuine Mercedes-spec filter and pan gasket fitted, the pan torqued back up, and the box refilled with the correct ATF to the proper level following the fill procedure, with the fluid temperature checked so the level was set right. A road test followed to confirm the shifts were smooth and there was nothing dripping.
The outcome
Smooth, prompt shifts, no fluid under the car, fresh fluid at the correct level, and the leak fixed. The E250 went home with the transmission back to spec. A leaking pan gasket drops the level and a box run low or on degraded fluid wears its clutches, so resealing it and doing the fluid and filter rather than topping it up protected the box and put the shifting right.
