Non-watermarked manual: https://archive.org/details/zaxxon-sega
@Michael B, I don't think there is a bad copy, it's more likely that you missed a crucial step. The following instructions for finishing level 8 work with every disk image I've tried:
1. Destroy the eggs until there are none left.
2. Collect the flashing asterisk shaped treasure near the top of the level (with a white hat) if you haven't yet. To do this you will need to carefully sneak into its location with your hat extended (the hat and "tongue" can move through red walls without harming you).
3. Lose your hat by touching one of the centipede bugs or the dark green block (near where you are dropped off at the start of level 4).
4. With these conditions fulfilled the bird will come and pick you up. Go to the position where you were dropped off at level 4. Wait for a bird to come from the right and hitch your ride.
After completing this level the game will restart but will be much harder: the game will no longer limit the amount of "woka woka" enemies, and a new one hatches every 30 seconds or so, so good luck :)
I saw this game being demoed in an electronic store when I was a kid and it's what made me convince my parents to get an Atari 800.
Incroyable!! Merci pour la numérisation de la pochette et du mode d'emploi. On approche bientôt de l'archivage complet de la collection HATIER (hors collaboration avec ATARI France) pour l'Atari 8-Bit. :D