An oversized hex socket should work.

I'm going to head to HD today and get as close a Torx driver as I can find that will fit in the bolt. I'll try that today. I also ordered this set of multi spline extractors:
https://www.amazon.com/Irwin-Tools-53227-Multi-Spline-Extractor/dp/B0002SRG66/

With the multi spline extractors, do I need to drill out the bolt head first? I guess I'd have to remove the heater prior to drilling. Although I may be able to use my Skewdriver offset/angled attachment to get in there without removing the heater...

I would drill nothing and try some of the smaller bits in the hex hole before opening it up. There might not be that much torque.

Harbor freight sells a small right angle pneumatic drill that has a jacobs chuck. It's cheap and pretty slick. Might help with clearance?

Tony, I believe it says “7/32 drill” on the side of the one on the top row 2nd from right. To my naked eye it looks like all the ones on the top row are the same size but I could be wrong.

John,

Do you know what socket size is used for the smallest extractor in the red case? Thanks.

Tony

13mm socket.

Thanks for all the help guys. I got the bolt out without using an extractor. I think the bolts are supposed to be 6mm (?) but mine are 5mm. I went to Home Depot and grabbed a brand new 5mm driver that was obviously totally perfect. After letting the PB Blaster soak all night I wrapped the new driver in aluminum foil until it was as thick as possible but I could jam the driver into the bolt head. There was barely any movement. It took a lot of torque with the socket but the bolt finally turned without completely stripping. Success! And I still have the extractor kit on the way for future problem bolts I know I will encounter.

I couldn’t have done it without you guys. Thanks again!

Outstanding!

I hope your chin was a bit higher after you achieved the goal that you set out to accomplish! I always over do the bravado when I solve/fix/vanquish something. This Bud's for you!

Btw, consulting the PET, the bolts that secure the WUR should be M6 x 60mm but the ones securing mine were much shorter, around 40mm. Based on the depth of the threads that the WUR mounts into, 60mm would be too long. 50mm might work. I’m awaiting the new bolts that Tony is sending and I’ll report back on the length in case anyone else needs to replace these bolts in the future.

Specific bolt length.........
 

Ethan,

Your information is vague. The length of the Allen bolts needed depends on your specific WUR. For example, a WUR-045 has a base thickness of 36 mm and uses 45-mm long bolts. In your case, WUR-090 has about 30-mm base thickness and will need a 40-mm long bolts.

BTW, I mailed the two (2) 40-mm Allen bolts and an 8-mm x 8-mm adaptor yesterday. They are not brand new but in very good condition. The hardwares are FREE and reimburse me with just the cost of postage. Pay me later after the car is running or you get everything for FREE.

You could use a temporary bolt just to secure the WUR in place to do your testing. And replace the bolt/s when the replacements come in. Sears hardware store has a lot of good metric nuts/bolts inventory. Or go to Fastenal or to one of your local auto parts stores. The heat wave in our area is gone. So better hurry up the work and drive this car like you stole it.

Tony

Thanks, Tony! I had no idea that there were different thicknesses of WURs. It's odd that the PET seems to indicate they are 60mm bolts when that is clearly not the case. And thanks again for sending the hardware.

A note to everyone else: Tony has been fantastic with his shipment and support of the rebuilt WUR I purchased from him. His reputation is excellent, of course, but I'll add my kudos. He has gone, and continues to go, above and beyond anything expected. And his knowledge of CIS is excellent. I would recommend him and his WURs to anyone who needs one!

What is countersunk? Flush?
Why can't the extractor socket work?
Looks like a regular bolt head to me.

The extractor socket would have worked. I managed to get the bolt out without it fortunately.

Pic is deceptive. It is a round female allen bolt head.

I have dealt with messed up fasteners many times, and in many ways. The extractor set that JW shows is the best design I have found. It is from Snap-On, but not as expensive as you might think. Another trick I recommend, if you have to drill a fastener out, is to get a set of reverse drill bits. Use a punch to ensure the bit is centered. Start with the smallest drill bit and then go progressively larger until you can get one of those extractors to fit the drilled hole. In my experience, the reverse drill bit backs the fastener out, without having to use one of the extractors, about half the time.

You sure about that?
That star looks 100% protruding towards the camera, not away.

So everyone clearly sees a cap head bolt and provided methods to get it out ONLY for cap head bolts, but you argue it’s a hex.

It's one of those optical delusions.