Usually at 80% none valve is damaged.
You are able to find that out with cylinder pressure check!
As for do it yourdelf repair I would suggest to be adviced with opel repair software or autodata with 135 euros each
OPEL PARTS GREECE
E-mail: alpharm@otenet. Gr
Online: Opelparts@hotmail. Com
Friday, May 9th, 2008 AT 1:41 AM