The brief
Mr Boo brought his 520i in for a service with an automatic transmission fluid change. Looking after the gearbox is the cheapest insurance there is, and at a higher mileage it's the right time to do the fluid and a couple of related items as preventive maintenance. The automatic transmission fluid lubricates, cools, and does the hydraulic work of every shift, and it degrades with heat and miles, so it gets refreshed on schedule, along with the transmission filter and the pan. The transmission oil cooler keeps that fluid at the right temperature, and at higher mileage it's worth renewing it as a preventive step, especially on the second fluid change, so it doesn't fail down the road and overheat the box. Doing the lot together keeps the gearbox protected.
The diagnosis
On the ramp the 520i came up due for its service items, and on the transmission side the fluid, filter and pan were due, with the transmission oil cooler worth renewing as preventive maintenance at the mileage. Nothing was failing, this was looking after a healthy car before anything went wrong. So it was a service plus a transmission fluid change with a new filter and pan, and the transmission oil cooler renewed as a preventive step.
The work
The engine oil and filter were changed and the other filters and fluids checked and topped. On the transmission, the pan was replaced, the old fluid drained, the transmission filter renewed, and the transmission oil cooler replaced with a genuine BMW-spec unit. The box was refilled with the correct BMW fluid to the right level at the right temperature, the way it wants it, and the adaptations relearned. The brakes, suspension and tyres were inspected while it was up. A road test confirmed a clean start, smooth running, crisp shifts, the gearbox temperature steady, and no warning lights.
The outcome
Fresh oil and filters, fresh transmission fluid with a new filter and pan, a new transmission oil cooler, the gearbox running cool and shifting crisp, and no warning lights. Mr Boo got the 520i back serviced and the gearbox looked after for the long run. Doing the cooler with the fluid change is preventive maintenance done right, because a failed cooler down the road costs a lot more than renewing it now.