Missing cog?

[Bulbatron]

VERY MINOR PUZZLE-RELATED SPOILERS AHEAD!

I'm playing the Mac version.

I didn't know whether to put this in the help/tips section or this one. I'm not sure whether problem is me or the game.

Basically, I'm in the machine room trying to get the lift started. I've put all the rods into the machine and used the levers.

I also have two cogs in the machine, but I can't find the third - the one which goes on the rightmost end of the gears mechanism. I've got the inserted the left and middle cog.

I've just spent a couple of hours searching the machine rooms for the third cog, but I'm beginning to think I may have been the victim of a bug.

In the end I had to swallow my pride and try YouTube. As far as I can tell, the right-most cog can be found next to the machine where the rods go, but there doesn't seem to be any sign of the cog on my game.

Can anybody offer any assistance? I really have looked everywhere - including the ceiling!

Thanks.