Defective/corroded bolt on Arnott strut
 

I had a leaky air spring a while back and decided to replace the fronts as a pair.
The driver side had the BMW original strut which was leaking. The passenger side was an Arnott and I am not sure it was leaking too but I went ahead with the replacement anyway. Now, on this passenger side, the strut went in easy. I torqued the three bolts on top (engine compartment area) and then moved back underneath to finish up and put the wheel back. While working on this I heard a piece of metal shot up. It hit the hood and then back in the engine compartment. I looked around to figure out what just had happened and I didn't notice anything at that point. I thought maybe something from the street flew over but it was a quiet afternoon and nobody around me. Anyway, after I finished with the wheel and I went back and look for the piece of metal or clues. It didn't take long since I only touched three bolts on that area. I checked that first.
One nut and its own bolt were gone. I found it on the tranny heat exchanger valve. Here is where it snapped and why:

http://i695.photobucket.com/albums/v...ps8zz2wddm.jpg

http://i695.photobucket.com/albums/v...ps4ihn7lfi.jpg

http://i695.photobucket.com/albums/v...psmhlfbkqs.jpg

The good thing is that I don't have to take the strut out. The bolt is removable from the strut assembly and I can use one from the old strut.
The difficult part is that the bolt seems to be very hard metal and I cannot use normal drill bits to drill through.
Any suggestion on what bit I should use? Cobalt? I have a bolt extractor but I need to drill a hole first.

I tried Cobalt bit and nothing. Any help appreciated.

I also called Arnott and they want me to ship it back but too much hassle...

What did you torque it to?

These are usually torqued to around 20 ft/lbs.

Try using a small punch so you have an indentation and then you may be able to use a small bit to get a 'starter' hole so larger size drills have somthing to bite into. Don't need much depth. You can then step up in stages until you have the size hole you need. Have to be careful as the small drill bits are easy to break when the metal is hard. The risk doing this is that the small bits break of flush and complicate the problem.

Yeah, 34NM.

That's what I did. I used a 3 mm bit and I only made a 'dent' the diameter of the bit but I guess the drill bit just got dull immediately.

I tried smaller bits on my son's 330 rusted bolt and I ran exactly in what you are describing. That's the reason I am asking for tips because I don't want to go through the same bad experience. I ended up buying a used wheel carrier. then.

Anything I can think of that will remove it needs a hole in the bolt . One solution would be to remove the strut and take it to a machine shop. New Cobalt drill bit should have done the trick.

I took it today an indy shop this morning and they tried a few different drill bits and no success. It seems like a very strong bolt material. I will have to ship it back to rock auto unfortunately.
I found online a Rescue bit I could try. Any thoughts?

You were right. Before to send it to rockauto I decided to try one more time. The Cobalt bolt worked well at low speed. It seems like the Cobalt bit I used initially was coated Cobalt only.
So, I managed to go through the bolt all the way on the other side. The bolt wan't all the way in to the bottom. The problem I have right now is the red loctite. The bolt doesn't move at all. I was looking for a chemical to dissolve the loctite but I am not sure if it will work. I cannot apply much heat unfortunately. I poor acetone in the hole to soak the threads hoping it will act as a solvent.