Micarta can absorb tiny amounts of water that may be difficult to measure. I have some stuff that is water stained, too, thru a few of it's layers, indicating that the moisture penetrated into it. I often wet sand when shaping Micarta and wipe down with Denatured alcohol and let dry, then do the final shaping/sanding after the surface has relaxed a bit and equalized. The fibers can absorb some liquid and expand slightly, then contract when it dries out. Something like G Carta or my homemade micarta type material, or Damagrip, will often absorb more moisture than commercially made Micarta/Phenolic laminates, too. I often let a handle with those materials dry out for a while and then flush everything up with regards to the tang and pins/lanyard tubing once it's dry.
Tung Oil or a "drying oil" like Tru Oil is good for micarta or G10 to protect those materials. It will coat the surface, soak in very slightly and then dry/harden over the next few days. Multiple coats can be built up as well. I usually do 2-3 coats when I make a knife in Micarta, 1-2 with G10 handles. I have hunting/fillet/kitchen knives I did with tung oil over the micarta and when they get nasty looking (dried blood, fish guts, etc), I wash with soap and water, and a quick coat on Tung oil (if it's needed) and it's back to looking like new! The Tung oil will build up over time, so I don't always have to redo the Tung oil each time if I build up a few coats first.
To protect the steel, mineral oil or a gun oil would be good, but gun oils probably aren't food safe!
Not sure if it's a folder of a fixed blade, but Tung oil will work on all handle materials. I epoxy my handle scales on and make sure I have good coverage and haven't had any rust issues; some of the blades are over 25 years old!
. To each.their own....