Old Crank

3-2 Catacombs, Leon's side of the long split (the blue-gem gate): the next gate's panel has no crank. One of the zombies (or armoured zombies) that attack when you reach the panel drops it.

Fit it on the crank-less panel near the spinning blades: it opens Helena's gate. She then opens Leon's last gate.

The split: Helena turns the cranks that open Leon's gates (twice, with zombies and a Bloodshot) and can shoot Leon's attackers from her side. Leon snipes the zombie turning the spear-trap crank. At the end of her route Helena finds 2 coffins: the left one holds 5,000 SP, the right one a snake. Leon can walk back down that path afterwards.