Too Much Sealant…I Hope.

Sounds like sealant to me. Some of it can be really difficult to get off. Have you tried Windsor and Newton Brush Cleaner and Restorer yet? That'll get just about anything off, with some time and effort. You'll want to make sure to wash the head thoroughly before doing a faceup afterwards though.

 

Printed resin has a lot more "texture", or grooves due the printing process, which allows for gunk to keep stuck inside better.
Also, 50% rubbing alcohol is waaaay too weak. You really need to use the 91% type, and you also need to use something that allows you to scrub (so don't just wipe with cotton pads, actually use a toothbrush or piece of magic eraser).
Regularly rinse with water while the head is still wet from the alcohol to actually wash off the residue...otherwise it just stays on the head.

You can also, carefully, use a toothpick to get inside the hard to reach areas (nostrils, inside of the ears, between the lips).

Some of these marks also disappear once you seal the head again.

 

It isn’t super caustic, but I have accidentally stripped the varnish from my table before, so you’ll want to make sure to use it over something safe. It can weaken plastics, but it takes a bit of soaking for that to happen, like days worth in my experience. It’s got an oily sort of texture, but it’s my go-to for super stick colors and sealants.

Like Ara said, it sounds like the sealant is stuck in the texture of the resin, so you should be able to get it off with time and the right tools I’ve also had pretty good luck with 91% isopropyl.

I usually use Dawn kitchen soap. I’ve never had any issues and it’s good at getting oils off. I just kinda slather it on my hands and then wash the head under running water until the soap is gone and the head feels clean once dry. When using the Winsor, it has a bit of an oily feeling to it and a specific smell, so you can tell if it’s on there still. Resin is a porous material, so it’ll absorb whatever you soak it in, to some extent.