With the pro's defeated...... or threatening large bills without promising success I returned to the attack myself.
Plan B:
I tried driving around with the other 4 bolts loosened (but not removed). I stayed on quiet roads and didn't do anything daft (initially). After about 5 miles of taking it steady I tried braking hard enough to deploy the ABS - several times, then some weaving and the latter eventually provoked some clonking - at which point I tightened the remaining bolts and went straight home to undo it..... or not as it turned out. Still stuck firm. Tried loosening the other bolts off, or doing them up really tight - no joy.
Plan C:
At this point I broke out the dremel and carbide burr to cut the rotating ring off and then attempted to use a proprietary removing tool. That failed as none of the sockets supplied in the set were the right size and even after reducing it a bit with the dremel and putting some notches in it I couldn't get the tool to bite as the bolt head was so hard.
Plan D:
Found a bit of thick wall tube that just fitted over the bolt head. I welded a big nut on one end of it then trimmed it as short as possible. Then managed to weld it to the bolt head by working down the inside of the tube. Not easy as the MIG torch is not much smaller than the pipe ID. Was hoping the considerable heat might help too. Seemed like it might almost work as I could really put some torque into it finally, the 3' breaker bar flexing considerably - before the weld broke
Plan E:
As my tube was now full of weld it wasn't re-usable. I found the biggest nut/socket combination that just fitted into the hole in the wheel and used the socket as a jig to hold the nut while I tacked it. Then retrieved the socket and welded it properly. Access was better this way. Once again I was able to get enough torque into the bolt to flex the breaker bar considerably, but once again, the weld broke. Bolt is just too damn tight or corroded.
Plan F:
Desperate measures. Break out the die grinder and carbide burrs. Slow progress, noisy, lots of sharp swarf, grinder (electric one) kicks like a mule. Took about 45 minutes to chop the head down to the point where I could break the bolt by pulling on the wheel. The stump unscrewed from the hub with a pair of pliers - not corroded, just TIGHT.
So success at last. A few minor marks on the wheel, but mostly in the bolt hole. No damage to the surface where the bolt clamps it. Reassembled with a new bolt and some copper slip after cleaning up the wheel/disc faces.
One to to go. May go direct to plan F for this one, though the best burr I have is showing signs of attrition.
Nick