This page now covers the following:
Although the drain plugs are hard to get to, do not jack your smart up to access it.
This will raise the fill hole and increase the capacity. If you really must jack it up,
level the car by jacking the front up level with the back.
Drive the car until it is at full operational temperature, this allows the fluid to
warm up and therefore flow better from the casing.
Undo the top drain plug first, there is 2 reasons for this:
It allows the fluid to flow out easily from the lower drain
If you take out the lower plug first and can't undo the top one because it is
seized or the head becomes damaged, you have no way to refill the transmission.
If you do the top plug first and you cannot open it, you have no problems,
you can sort it out in your own time.
Official Service Schedule For Gearbox Fluid
Smart's stance on this has always been the same. In their view, the transmission
fluid is a non service item and does not need changing for the entire life of the car.
It's not an oversight, this is what they have said in all of their cars since 1998.
They clearly don't have a clue and they should be ignored.
Evil's Recommended Service Schedule
Anything between 40 and 60 thousand miles will be fine.