And in those cases the correct information is usually extracted from either manufacturer or sometimes aftermarket.
E.g. zf tell you to change atf on their 6 and 8 spd every 100,000 kms,
While bmw, rolls royce, jag, chrysler etc are saying to never change, same when we see magna-steyr or ferguson transfer box in awd, the box manufacturer is speccing a 50,000 kms oil change while car brands are telling its never to be drained, toyota also pulled this BS with their automatic gearboxes, their dipsticks say to never change the atf, those who follow, spend nicely on either buying a repaired box or scrap the car.
It works both ways.
Its best to follow proven best practices collected from a spread of manufacturers. It really broadens your experience.
Best practice has a thin as possible oil in the system that provides least drag, optimum flow for better cooling and cleaning etc etc.
Btw your experience which is heavily based on weather seems like you deal with monograde oils.
Btw, lifetime fill is not limited to dct boxes only.
