88' 300E Steering Wheel...

[Californian SE]

So I'm trying to replace the cruise control stalk in the 300E, as it is broken.

I need to remove the steering wheel to do so... Luckily at the wrecker I could simply attack the black plastic trim and rip the cruise stalk out.
I, however, do not wish to attempt that on MY car!

I know you need to remove the main 10mm nut holding it on... but someone has tried before me and left rather a burred nut to deal with.

Presuming I can get a replacement nut what is the best way to go about removing it, using the 10mm hex is simply not an option, as it's a 12mm hole now!

Cheers