Making Boiling Oil more useful (rather than replacing it entirely)

Assuming that Boiling Oil doesn't get replaced entirely, what would make it more effective?

Some suggestions:

• Reduce research time from 40 seconds to 1 second (if it is ever effective, this tech is only effective for a brief window in the castle age anyway, before opponents get Capped or Siege Rams. This would make it effective for a full 39 extra seconds of game time..lol. And people could wait to research it until Rams were in sight).
• Have it make all castle arrows INCLUDING EXTRA ARROWS (or at least extra arrows) do +0 melee damage thus making all arrows do +3 damage to rams. (This would just be interesting a la the Chu Ko Nu doing hidden damage to Rams via their +0 melee damage and the rams -3 melee armor. Even a fully garrisoned castle with hand cannoneers would still need 4 shots to kill a siege ram in the Imperial Age, so that seems hardly overpowered. And how often would you actually garrison hand cannoneers in a castle anyway?)
• Have it apply to the castles of the whole team once researched. (This might make it useful for a few civs like Teutons with longer range castles and garrisoned infantry extra arrows. Besides, oil is certainly a commodity that has affected all the civs of the world).
• Reduce cost from 200 wood/100 stone to 200 wood/25 gold (Afterall, oil doesn't cost stone anyway, it costs $ and boiling it would cost wood).

If ALL of the above suggested changes were implemented, would it be overpowered, about right, or still really weak/useless? I am not in the camp of those that think the Persians need a huge boost, so I don't think they necessarily need a new, awesome tech, but it would be nice if Boiling Oil at least had a niche. (If you think it already has a niche as is, please explain.) I personally think that even with these changes above it would not be used very often, except maybe when an opponent ram tries to solo a castle in the Castle Age (which is probably a good niche for it).