So it begs the question ??
What do you do if the transmission (caja automatica) or auto gearbox , as you call it in the UK has done say 150,000 miles, and has never been serviced , or even 275,000 !
Like I saw the other day, and the security cap lock plate was a factory production black 'un !
Which means it had never even been dipped.--ever! Oh lor!

Whazzup Doc?
You see often owners simply don't service a transmission until it shows a problem like poor shifting! Time for a service --wrong!
That's when they drive onto the forecourt with drivability issue.
Now back in "zee oulden days" with simple hydraulic transmission in Land Rovers, 123 Chassis MB's and Jags with Borg-e Warner boxes, simply shoving the selector from D to R at about 40 mph will fix it, plus a service, but nowadays the 7 speed technobox won't like that instant fix !.
Oh Lor!
Then a memorable one back in , "me yunger yurs years" as a service engineer with Leyland Bus.
In short London Country Bus en route to LHR on the M4, with an Olympian Decker coach fully loaded at about 50 mph , dropped the prop shaft onto the road when the driver
MANAGED to select reverse without really trying!
Enough I bet to wake up all the international; visitors about to leave the UK.

I bet it scared the bejeezus out of 'em.
Talk about going out with a bang!

Tuercas viejas
p.s telling my lovely American missus about that incident a few years ago she asked
"Did someone get the shaft on that 'un?" 
TWA humour!