What would happen if you didn't put the hto additive in the 10w30 that's I'm the hydraulic system. Would the oil foam up once it gets hot and cause the hydraulics to not function properly or does it just preserve the run life
Reportedly it would foam up and not lift very well. When oil foams it introduces air (which is compressible). I've personally always used it so I can't say from first hand experience, but that's the conventional wisdom from other owners. I haven't read anything about it being used to extend life.
The other risk is chatter from the wet brakes...or so I have heard.
Its a zink anti wear/antifoaming additive, which helps preserve run life. Its only a 1 to 20 ratio, so not really needed for just a top up of your hydraulics. Relatively cheap in comparison to damaging your pumps. Not using HTO additive would not cause any immediate issues, as none of the newer models take the HTO additive anymore.