I encountered a dead end. After I returned from the skull island I cannot buy alcohol for the jet pack anymore. Before trader Bob aked me for the ID. Now I have the ID but I cannot buy the alcohol. He tells me that I cannot afford it. I spent times reviewing the walkthroughs but I didn't miss anything. So it seems to be a bug.
Additionally I violated the saving rules and overwrote my save games. If you have a savegame after the skull island plz send it to wollig-at-gmx.de.
It's been too long since I played the game, so I don't remember this puzzle. But I've seen one hints page for the game which claims to answer the question, "Where do I get the money for the alcohol?"
