That's correct... all 757-224s, all 757-324s and most 757-33Ns have the RB211-535E4B variant. A handful of the ex-ATA 757-33N were still certified as the -E4C variant as recently as a year or two ago, but that might have lapsed as there's no structural difference between that and the E4B. The E4C was developed solely for ATA with a small thrust bump to enable 753 operations from MDW, and carried over after CO picked up those frames following the dissolution of TZ.

In 2019, StandardAero at SKF won the TotalCare contract for the RB211 fleet through its end of service life, and UA sends its motors there for overhauls.