I don't own a Fin Bore but a 6" Sub Zero.... going on the third season and never had any issues with it.... cuts through ice like butter
I never put any weight on when drilling, just let the blades do the job and when I reach water, I keep going an extra turn and then thrust downward to get the final piece of ice chipped.... then the plastic guard goes on it when not in use
Sounds like your blades took a beating from the jolt and warp them.... sharpening won't resolve the issue.... my advice is to put on another set
Leechman