I have a Packasport fiberglass car top carrier with a cylinder lock. The key has been lost. I ordered a new lock/key set from Packasport but am unable to remove the old one - the locking nut is rusted on. I've tried Linseed Oil and WD40 and still doesn't work.

My latest idea is to drill through the locking nut that is right next to the fiberglass wall of the carrier (drilling parallel to the wall, perpendicular to the surface of the locking nut) to create a gap and then just wedge the nut off using a chisel. I don't care about damaging the existing lock but I don't want to damage the fiberglass. However, when I tried this the drill would just slip right off the (very thin) nut surface.

Any ideas?

These car top carriers are expensive (about $1000) so worse comes to worst, I'll probably just live with not being able to lock it any longer.

Thanks!

Here's what it looks like: