Saving the threads, even if it were possible is a waste of time, because
the
treads have become aluminum oxide and have no residual strength anyway.
Next time use anti-sieze at assembly. Most likely the fault was
electrolysis, as they were probably diecast and zinc is often alloyed with
the aluminum to promote flow in the mold. In the presence of water, the
unit becomes thousands of little batteries.

On second inspection; if I can't get the bolts out, it looks like drilling
the next size and tapping won't work. I'll have to make all new. My version
will be a bit beefier. What's the best bolt for AL with an eye on
electrolysis? AL bolts are too soft in small sizes. Is stainless a good
choice? or maybe brass?

Karl

Karl,
I run into this all the time.. .. .. and I've found out that the best
solution (if you have the room) is to drill, tap and install a
stainless Helicoil. A bit pricey, but ya only do it once.
Ken.