I recently embarked on upgrades to my Fender Classic Series '70s Stratocaster® Electric Guitar. I noticed how one string was changing pitch after using the tremolo. A worn groove in the bridge saddle was allowing that string to stick. There was also a sticking groove in the guitar nut that would release string tension with a "ping" and thus detune. So I ended up replacing the Fender stamped metal saddles with Graph Tech String Saver Saddles with TPFE (Teflon lubricant). I also replaced the string trees and guitar nut with TUSQ XL, also with TPFE, which has the lowest coefficient of friction of any material. Problem solved.