replace them mate, i learnt that the hard way when doing the head gasket on my clio....i stripped it all down....easy.... came to put it back together and i am not kidding, i got to the last bolt started to tourq it and SNAP! had to take the rest of the bolts out, drill the snapped piece out and then re-tap a new thread for some NEW bolts.....i wont do that again, always buy new.