I remember many years ago when the sprinters first came out the manual said transmission change and 70,000 miles I believe and that was it never said another word but doing it again
It's worse than merely never saying another word about doing it again, it is very explicit, both in the Owner's Manual and in the Scheduled Maintenance Manual:
From the Owner's manual...
From the Scheduled Maintenance Manual. where it has just the one page for recording all of the transmission maintenance for the life of the vehicle...
Then they came out with a TSB that said change it
every 60,00 miles, and a year after that came out with one that said
every 50,000 miles.
Guess our Transit is the only one with a sprinter transmission, lol. Cause that sounds like what's going on with ours. And I wouldn't mind a regular flush/change every 35k...but it is a sealed transmission not supposed to be serviced until 150k....
Well, it won't hurt it to change the fluid early. Once the fluid starts breaking down, it goes quick, and shortens the life of the transmission. If the transmission fluid gets too hot, it begins to rapidly break down. RLENT has a temperature gauge for both his engine coolant and his transmission fluid in the transmission, and it was surprising to see just how much hotter the transmission fluid can get than the engine coolant when climbing grades in the summer (at 75 ambient or hotter). Grades in the Appalachians and the Rockies, and elsewhere. The engine coolant tempt might be 200-210 F on an uphill grade, but the transmission coolant might be 260 F or hotter.
ATF is designed to operate and perform best within the range of 175-210 F. For every 20 degree increase in fluid temperature beyond the normal range, the life of the fluid is cut roughly in half. So if you do a lot of towing or you are routinely loaded near the max GVWR, you should probably change your fluid at least at half the normal interval, if not sooner. That or you should consider an external transmission cooler.
If it were me, I'd change it out every 50,000 miles and I'd use a can of BG ATC+ in every change.