about harm of oil on thread (especially aluminum)

[Konstantine Bogach]

Second time I screwed the thread trying to torque a bolt to spec. I
don't remember what was the first time but this time it was 6mm bolt
holding turbo oli supply line on oil filter housing (aluminum).
Actually, I stripped the female thread in aluminum, of course.  I did
not reach the torque spec.  Later I found oil in the thread in
abundance.  Apparently,  deformation in material goes easier with
lubricant and the thread is stripped before reaching spec torque.  Does
anybody had such experience?
Is it well known to everyone except me?

I need an advice how to fix this situation.  I don't recall seeing
helicoil for 6mm thread. Does it exist? Stepped stud would be perfect
probably, but where can I get it fast is US?

Thank you in advance.

Konstantin Bogach.