I saw a suggestion somewhere that they implement a value/scale, let's call it an oath-'o'meter, like 'attitude' - that represents how well you are keeping to your oath - and if you violate the tenets of your oath, each violation removes some of this quantity , the size being dependent on the scale of transgression. So you might have one really terrible act that breaks it, or a series of smaller ones that eventyually break it. Rather than the current (often small seeming) infractions with mean you get visted by a death knight...
The way breaking your oath is described in the phb, it's not something that is supposed to be that rare. If you break your oath, you are supposed to seek absolution for it (from a cleric of the same faith or another paladin technically) to wash the "sin" away. You can only go "oathbreaker" if you aren't repentant for what you did.
The Oathbreaker Knight offers to listen to your confessions and offers absolution via a money exchange. It does emulate what a real life GM would do, but without any deity selection and not alignments.
