A lot of manufacturers say that the fluid is good for the life of thee transmission, they're right! Don't change it, expect it to go at about 100,000 miles and then your transmission is gone. Maybe 150. But not changing fluids definitely shortens the life.Below is what your transmission will look like when run low on oil and contaminated with water. This is the transmission in my 2000 Jetta TDI in 2011 at about 250k miles with no changes or top-offs. The 5th gear Slider and Hub were worn so bad it jumped out of gear with no warning and I never could get it to stay in 5th gear again. I ran a 5th gear out of a gasser transmission until I found a replacement. Today, after several flush changes, the transmission is doing fine at about 380k miles on it (my son owns now). The last two changes, I put Penn Syncromesh in it.
If I could ever buy a new car, it would get all fluids changed the first week. All of it. I did an oil change on my motorcycle at 30 miles (half an hour ride from brand new) and seeing what came out, I wouldn't want that in there. All the metallic residue of gears breaking in made the oil sparkle.