Ah, yes! Back in Best way to fix a broken but functional program?
I posed something similar. The jist of the responses was to "redo the damn thing"! As I did. Time proved that rebuilding it was far easier than undersanding not only the style of the code but the bit of history in which it was writen.
Pits and bieces of it I was able to cannibilize, sure. But in rewriting it I became very familliar in what it was doing and how, and made it more stable and smaller than it was before.
As with anything like this, look at the thing before you ditch it all together. USD $0.02.
Apply yourself to new problems without preparation, develop confidence in your ability to to meet situations as they arrise.