Corrosive

In the flashback (2014): Cargo Bay S2 ×3 (table behind the green gate) and Store Room S2 ×1. In the present: Lounge 2F ×3 (in the picture-puzzle safe), Guest Room 2F ×1 (foot of the bed), Sick Bay 3F ×1 (NE medicine cabinet) and Recreation Room 1F ×1 (bench by the door; not on Madhouse).

Melts padlocks and wall panels. In the present:

• 3F Control Room → Main Corridor.
• 2F Main Corridor → south half of the Bunk Room (Captain's Cabin Locker Key).
• 1F Main Corridor → Recreation Room (Backpack #3).
• Workers Access Passage 2 panel (S2) → Antique Coin #18.
• Cargo Bay panel (S2).

In the flashback they open the door to the No. 2 Engine Room, the Store Room and two panels holding Remote Bombs.

Lounge safe: rotate or flip each of the 3 pictures on the right wall until it matches its twin on the left wall. The present has 6 for 5 uses: one is spare.