OK, this one should be (and has been) quite simple but here comes that horrible word "however". I killed the two lizards with the target lizard early on but the target lizard slithered away while some bloodflies (I think) attacked me. I've been searching and searching but have not rediscovered this lizard. Very minor XP loss (this and finding boat plans) but still, does anyone have an idea why this might be happening? Random bug?

I was afraid of that. Oh well.

The thing is, though, that usually when a monster attacks me from inside a rock (or in one case, a bow-armed bandit), I just save, close down the game, and reload and it is fixed.

If you just want to close the quest you could always use Marvin mode to add the tool you're missing to your inventory.

I'm not sure its worth the effort but, yes, this would be a case where I'd be comfortable doing it. Never done it so I'd have to research past posts and all that for a handful of experience points.