Disarming (Again!): in 1e/OSRIC

I spend an inordinate amount of my idle time thinking of ways to do various combat maneuvers in D&D. Since I'm about to start a 1e campaign (in the Forgotten Realms, by request, no less) I've once again, headed down that particular rabbit hole.

Here's my new Disarm maneuver for AD&D:

Disarm

A Fighter attempting to disarm an opponent must state his/her intent before making their "to hit" roll.

If the defender is 3 or more levels higher than the attacker, then the attempt succeeds on a roll of a true 20.

If the defender is within 2 levels of the attacker, higher or lower, then the attempt succeeds on the roll of a true 19, or 20.

If the attacker is 3 or more levels higher than the defender, then success is indicated on a true 18-20.

If the attacker is 8 or more levels higher, then a true 17-20 succeeds.

In all cases, the target number must still be a "hit" vs. the defender's AC, save that a true 20 will always succeed.

Whether or not the attempt to disarm succeeds, no damage will be taken by the defender. 

There. I think that does everything I want it to do. I considered altering the target number if a Large Shield was employed by the defender, but then I would have to consider the number of opponents attacking, nearby defenders, etc.

Damn! I forgot about Monks! But, I'll think about that later.