I'd suggest it was condensation forming on the inside at Night. Sydney is very Humid, Plenty of sheds drip Moisture at Night from the support Beams from the Underside of the Roof. A lot of dusts are either acid or alkaline. Higher up in a shed stays a bit warmer. because Hot Air rises. Most intricate things when stored need special Preparation to prevent surface rust activity and oxidation of waxes and Oils. If you have reground crankshafts and newly Machined gears etc sitting on shelves they all need protection. Oils and waxes oxidise and Leather rots. Bat $#!t is really bad at damaging surfaces (Paint and Plating). Rubber goes hard and cracks I have ONE (only) Sealed and well insulated room where stuff can be left for ages But everywhere else You have to cover if and Polish the surfaces to Protect the Finishes. Nickel and chrome are Both Porous enough to form rust below the Plating. Zinc gives a Galvanic Protection but it's soft and abrades easily. Stuff left sitting can deteriorate badly of not looked after Properly. IF it's in a bin makes sure there are holes in the Bottom in case some water gets in there. Just one rusted tooth on a Gear Makes it useless. Beds on Lathes, Mills and machine grinders must be cared for Meticulously or they lose their accuracy. Bare Metal ready to Paint should be coated with an etch or appropriate surface chemical as soon as it cleaned and dried. Don't paint over rust. Nev