Regarding the guild master william case, there are already few report in the technical problem sub forum. You can try check out threads over there for solution
The zappelin parts had nothing to do with your baal case. There total of 9 zappelin parts, where if you found all and return them, you get extra reward on exp. That it
As for the amon, if you able to enter baal's cave, you should find it infested with black ring soldiers, where amon is like a small troop leader. After you kill him, he should drop a key where you can use it to access baal's lair. If you had a save before entering the cave, try reload and retry again. If you cant find amon in the cave, guess you need to send in your save file for a fix.
