Rear lower suspension arm problem

[beamertheone]

Taking the rear subframe out for repairs and painting etc.
When removing the lower suspension arms, the bolts holding the damper/shock absorber in position I snapped one bolt on one arm and stripped the threads on the other because the bolts totally corroded in the alloy of the arms. Drilled and tapped out the remains of the snapped bolt.
Re-torquing the new bolts before fully assembling the frame, the threads failed.
As these arms are difficult to find in the UK. Is there any issue in drilling the threaded hole out to 12mm dia, then use high tensile socket cap screws of 12.9 quality and high tensile nuts to hold the damper/shock absorber in the arm.

Read someone suggest to use a Helicoil thread insert, but I've only used these in a blind hole not a through hole. But then these have the danger of following the bolt on removal in future and may do more damage against the damper/shock absorber bush.