I have a 2013 4runner at 100k miles. I called one large Toyota dealer and they said the transmission is universal sealed, or something like that, and it should never need the oil in it changed unless there is an issue. I called another Toyota dealer and they said it needs it($300). Do I need it? Opinions welcome

I looked through the maintenance manual and it is all over the place depending on how often you are off-road. I am on dirt roads maybe 5-6 times/year.

Most here on the forum would recommend changing it including me.

helpful writeup
Transmission Fluid Change procedure

helpful video
https://www.youtube.com/watch?v=PPhiIxs0VQM&feature=youtu.be

Do it.

Also do the t-case and diffs if you haven't already.

A "sealed" unit is a misnomer, they have to get fluid in and out somehow. The notion that changing transmission fluid at "high mileage" causes damage is also incorrect, and shows that whomever propagates that myth doesn't understand how autos actually work. Long story short, changing your transmission fluid won't damage your transmission, but it could expose any slippage that was being masked by the old fluid. Old fluid -> more friction -> less slipping. New fluid -> less friction -> more slipping. Again, what causes the slipping is wear in the transmission, not a property of the fluid.

Have your fluid and filter changed. It may not be relatively cheap, but it will ensure your transmission lasts (at least) another 100k miles. There's no reason to believe your current fluid would be masking any wear-caused slippage in your transmission.

There's no evidence I'm aware of that it has any value in prolonging the life of the transmission. You can look around and find that there are basically no failures. So... if it makes you feel better, go for it. It probably won't have any effect on the life of the transmission.

Unless you put the wrong fluid back in, which is farily common both on here and at dealerships. You want Toyota WS. Toyota WS is not backward compatible with T-IV, so if the bottle says it meets both standards, that's not possible. I mean that literally. They have different viscosity that are not overlapping, so one fluid cannot be both standards. Toyota WS is not expensive and there's no reason to use the wrong fluid.

Good luck.