Ryan won an ERA title with Houston in a year when he was 8-16. Are you asking for guys who won in the year immediately folllowing their departure? I'll guess Seaver is one.
But Prior is better than Dave Williams, Jose Lima or any of the other retreads we have run out there in the past two years. My point is that we should take a flyer on an oft-injured youngster who may yet recover rather than an aging vet who never really had it.