+1 to AVB on screw extractors. The tapered left hand spiral flute 'ezy out' type belong in the bin, IMHO.
If they don't strip out the hole in the screw, they break off, and you then have a very hard piece of steel wedged in the screw. Which is just about impossible to drill out, even with a tungsten carbide bit.
The only screw extractor types I have had any success with, are those with a parallel splined business end. These are available from automotive trade suppliers, but hard to find.
It is possible to chemically remove busted off steel screws/bolts from aluminium components [without any damage to the internal thread], but it's just not worth going to such lengths on a Victa!
Simpler to drill out, and re-tap to a larger size, or install a stainless coil insert [Heli-coil, Re-coil etc].
