so far i descended to level 12 and found and engine which the voice in dreams told me about. so i need 4 components to fix it . i fall down to level 13, found TONS of junk and metal scrap and gathered 3 components - the infuser, the bladed gear and a piece of ore. but even after searching everything i can not find the fourth thing. by the way i found a button in upper-left corner which does nothing when pressed.
also on level 12 i see 3 doors, all require gear keys but i have none.
i am sure i examined all wall on available space on 12-13 but not found any switches or something.
help plz

I've checked one of my later saves, and the component you seem to be missing is a small gear. It's not the bladed gear but a separate item, and it's also found on the floor of level 13. Check around there, and pay extra attention to corners and walls that have shelves in them. (I missed those the first time around.)

thank you,i seems that i already had this gear but it just not fit in place for some reason, now it worked.
but still question remains - can you open those three doors on level 12 at all?

You can open them but you don't really get anything. I've never opened one but heard that you can get keys from some of the spawned enemies after the boss is activated, the stuff in them is apparently just general resources like healing potions.

The stuff behind those doors are weapons that deal lightning damage, which is effective against the final boss. And yes, you get in there from keys that random enemies drop during the final boss fight.

There are two buttons that appear to do nothing on 13' but they are like the other combo switches in the game. When both are pressed, the no admittance area opens up to reveal the last crystal room & treasury, and something else is hiding in there too.

All right, I'm stuck here also. I really think what I'm missing is the bladed gear - it seems to be easily spotted, the guys in the Grimrock forum insist, but I did not find it. I've been searching level 13 with a magnifying glass, have consulted the gamebanshee walkthrough, still nothing. Can someone help?

/edit: Forget it. I did the same mistake. I didn't miss the bladed gear, but the steel one. Now on to the final fight!