Sorry to hear about your current plight. I will share with the forum a few techniques that I developed to avoid rounding off allen head bolts (AKA: Cheese Heads) as well as contending with one when it is rounded off.

The Loosening/Removing technique:

1. Feel for the grip of the allen bit, it should be fully seated in the bolt head (clear debris as needed)
2. Begin by applying slow, steady pressure to the tool you are loosening the bolt with.
3. Feel the bolt and the allen drive, if you sense the allen drive is just rotating STOP
4. Reverse direction and tighten it until you hear the bolt CREAK
5. Again with slow steady pressure try loosening the bolt, if the tool begins to rotate without hearing the bolt creak STOP.
6. FOR STUCK FAN BOLTS:
7. A block of wood (oak flooring material has been my choice) placed on the radiator surface will give you sufficient area to pry against without damaging the radiator.
8. Place a bent end pry bar against the wood then pry against the allen drive socket end in order to create more inward force
9. Again with slow steady pressure try loosening the bolt, if the tool begins to rotate without hearing the bolt break free it is “ALTERNATIVE METHOD TIME”

The Alternative Method:
Requires the use if a 90 degree high speed device (Die Grinder with Rounded end Bits)

1. R&R Radiator
2. Place a ½ rounded end bit (small flute) into the to die grinder
3. With care and caution (avoid tool chatter) begin to grind the center of the head
4. Once you have established the pattern for the bit continue grinding
5. Grind deep enough so the fan just falls off OR
6. Grind deep enough and then pry the fan off

The Avoidance technique:

1. The bolt securing the fan spins on it center axis
2. It does not require excess pressure to hold the fan in place
3. Once the bolt is seated, give it a little more torque (1/8 of a turn-MAX)

When accessible allen bolts develop problems:

• For 5mm allen bolts hammer a 10mm 10 point socket onto the bolt head
• For 6mm allen bolts hammer a 12mm 12 point socket onto the bolt head

FWIW:

• Some Intake bolts will simply break due to electrolysis, break them and move on
• A ¼ drive allen drive socket works best for the Air injection pumps on 116/117
• A Micro-torch and Zepreserve work well on stubborn distributor bolts
• When attacking broken wheel studs, cobalt drill bits cut well at 75 to125 RPM’s
• Metal curly cues are your visual evidence that a drill bit is working properly