even if you could last the entire life of the vx with that transmission fluid.. why take the risk.. you can relatively easily drain about 6-7 quarts of the fluid and refill it on your own
http://www.antiquecaterpillar.org/vx...l/4L30E_01.asp

btw.. its no problem to just drain whats in the tank for the power steering then pour in new ATF (NOT POWER STEERING FLUID!) to refill it every few months isnt it... this will keep the fluid more or less fresh?