KTM125SX 02 cylinder head bolts

I have a KTM125SX-02 ,whilst tightening the cylinder head bolts to 25lbs as the workshop manual states the threads felt as if they were going to strip so I stopped,unfortunately when I rode the bike 1 bolt came right out with the inevitable water leak,I would like to know the best method of repair? shall I go for a helicoil? do you think 25lbs is the correct torque?
Can I re-use the rubber O-ring cylinder head gaskets?

I would appreciate your thoughts on my predicament

yours in sport
:D