You do not have to change the whole lock. Opel GT Source can rebuild the electrical part of your switch. Sending this piece of starter switch is easy and inexpensive in a padded envelope. Once you receive it back, add the relay (Otto Start) and you will be fine for the extended period of time.
Thread on the removal of ignition switch is here:
http://www.opelgt.com/forums/1a-star...h-removal.html