What do you guys make of this?

A couple of years ago I blew up my T25. I upgraded to an SBR exhaust manifold and EVOIII 16G. I did the recommended mod where one installs 4 bolts (exhaust manifold to turbo) instead of the OEM 3 bolts and 1 nut. I bought all brand new hardware from the dealer when I did this swap. I may have put 10K on the car since all this work was done – never winter driven - all hardware looks brand new

This week I start to install my new FP exhaust manifold. I warm the car to operating temperature to help with the removal of the 4 bolts and one snaps - 1/4" from the end – go figure . So I spend most of my evening drilling out this broken bolt only to get almost there (hole big enough to fit the eazy-out) and the easy-out snaps !! Wow, this bolt was tight!! So now I have an eazy-out acting like a wedge - great!! All this work was done with the turbo still on the car. So I pull the turbo hot side and 02 housing off and go see my neighbor who does HVAC. He pulls out the torch to heat things up. We get everything red hot with vicegrips on the exposed threads and this bolt wasn’t going anywhere. We did it three times and nothing. So finally he cuts / blasts out the remaining bolt and I'm left to retap the hole.

Now here’s the interesting thing. 3 out of the 4 bolts are stamped "11". One is not. Guess which one broke – you got it – the non "11" . All these were OEM right from Markham Mitsubishi.

Anyone come across this before?

Also, should I be worried about my newly taped hole M10X125?

I bought brand new grade 11 bolts for my manifold, and found the one break with very little force applied, maybe 20 ft lbs.