I'm too new to say I know, so I would definitely like to hear more about the "traditional Reform" positions, however...
It seems to me, that OSAS is obviously true from scripture.
What was decided about whom to place "in Christ" before the foundation of the world, didn't need to necessarily "make sense" in the traditional way sense is made, to any of us. So for a once saved man to turn back to sin without repentance before death, may be jumpimg to conclusions if you equate that with damnation. It wastes the blood of Jesus Christ for one thing, and it implies we are capable of some impressive omniscience for another.
Sinful behavior can be due to many things, medical infirmity being just one, and that isn't hard to imagine in today's degenerated & toxic environment. But spiritualy speaking, it could be God's way of denying that person an opportunity for spiritual pride that wouldn't wear well in heaven, or it could be a way of granting him suffering as judgement for something we'll NEVER know about, until all is made clear 'on that golden shore'.
As I understand it, we don't lose our salvation onced gained, we simply lose rewards TO BE gained that await us in heaven. God doesn't save ya, then throw ya back.. not spiritualy. I mean Lazarus was physicaly resurrected, but he died again, right? Not right away, but eventualy. That doesn't imply he went to hell.
School me.