The Sterling aircraft that Prebennorholm is refering to was OY-SAS, which was the Valsan re-engining prototype, converted in October 1987 (as N727VA).
Going by the history of this aircraft, it's true that Sterling didn't retain it for long - it was leased out to Air Columbus after a year. It seems to have stayed with them until it found its way to Sun Country in 1994. It still flies with this airline, as N288SC, where it's known as a "Super 27" (current name for the Valsan conversion):
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Photo © Carlos Aleman
Sun Country also has four other ex-Sterling re-engined B727s : N290SC (ex OY-SAU), N284SC (ex OY-SBC), N285SC (ec OY-SBD), and N291SC (ex OY-SBO).