Stripped torx screw head
 

So I rounded out the head on one of torx screws that hold the airbag to the steering wheel on my '90 300se.

What is the best method to extract this screw so that I can replace it?

Thanks

You've got a problem here. If you can dismantle enough of the underdash to get access you could drill the head off the screw but it will be an awkward job, be very careful as you are likely to break drill bits.
Before you start make sure the airbag is disabled by disconnecting the car battery and waiting 15 mins for the capacitors to discharge.
George.

Using a junior hacksaw cut a notch in the top into which you can slip a chisel end or even a flat blade screwdriver which you can then use a 4lb hammer to twist the screw.
Saved me a million times. :)