If leak is between crank and seal itself, yes opt for the Fel Pro repair sleeve making sure to use lock tite.
If leak is between block and seal, replace seal only. They make a standard and premium seals, neither have proven 100% reliable. When doing clutches, if seal is dry we've opted to leave as is and not replace seal.
Back side of the seal, I use white lithium grease to fill the cavity full to prevent spring from flinging out. Oddly enough just had a pick up in for axle seals, previously installer did not use grease, spring had popped out and did damage to the bearing / axle face when it became lodged in outter edge of the bearing race.
Not sure why Ford did not make the rear main seal more like an axle seal with a steel lip so it's for sure in perfectly straight.
When removing old seal, be x x x tra careful not to damage / mark the crank itself, very common to see when we get a persistent leaker in someone else has had their hands on.