For most cars, it's part of 30k maintenance schedule

remember vw made a sealed transmission without dipstick for 2006 Jetta claiming never need service.  after a lot of failures due to lack of services, a few years later vw sent out a notice to owners saying it is now recommended that transmission be serviced at 40k interval.  problem came - because of "sealed", it's very hard to maintain, even for regular shops.  dealer charges about $600 for the service.