To be honest the remaining wall thickness after using an M8 x1,25 helicoil tap looks as though it will be rather thin from your photo. From the helicoil information it should be a minimum of 3,5mm but may not be enough if your assessment of the metal is correct.
Is there any mileage in machining out the existing poor thread and fitting a headed steel bush which has a plain 8mm diameter section, that is Loctited into the hole, and an M8 x 1,25 threaded end for a nut and washer?
Perhaps you could just fit a through bolt and Loctite that in position, I don't know how much room you have.
There does not look to be much metal to play with, it might require a bit more thought.
I hope it works out.
Neil
Forgot to say, the outside diameter of an M8 x1,25 Helicoil tap is 9,6mm, tapping drill size 8,4mm.
Edited By Neil A on 26/01/2021 22:40:33