the previous owner was running the synthetic XP-S 2 (yellow bottle) it's about 43.00 a gallon... i recently saw some new synthetic XP-S 2 in a black bottle it's 31.00 a gallon, what is the difference or is there something better i could run... right now my tanks are dry all lines new and waiting to be bled, I guess if i'm gonna change over i need to do it now..... Anybody have any good input?