I've used goo gone and oxy clean, I find CIF gives the best results and it's a cheaper initial investment. If you use the goo gone method I’d still follow up with CIF to rinse it off.
To start CIF and Vim are the same thing. Make sure to get CREAM kitchen cleaner version. There's 2 uses. Gettiting glue out of the hair, and out from inside the head. Glove up it's bad for your skin!
#1) Removing glue from hair. Scrub, brush with a comb, then rinse. Only use cold/room temperature water. Repeat until you get a bit of lather. CIF/Vim doesn't really sud up a lot but you'll see the hair get less sticky. If you spray goo gone (generously) on the hair first, let it sit for an hour before you scrub.
The CIF/vim will leave reside! To get it out shampoo works best. Scrub, brush, rinse until you get a lather going. Again cold water only.
I recommend sectioning the top and bottom half of the head when you scrub. You may need to divide the top of the head into more sections to preserve thatching
Both cif and shampoo took around 2-5 scrubs.
#2) Remove excess glue from the head. Squirt generously to cover the glue inside. Leave the head upside down overnight, then rinse it out and use thin pliers to get the big chunks out. I found it best to squish the head to get chunks to break off.
Some glue will remain stuck between the plugs though it shouldn't cause much issue. A few odd strands of hair may come out. Long as it's not a whole plug don't worry about rerooting it back in.
After removing the glue AVOID boiling water on the scalp. If you need to restyle keep cold water handy. If you need to boil wash step#2 should prevent excessive glue seepage occuring from a one time boil.
Lastly I recommend cutting off the T prongs at the base of the neck peg before putting the head back on. Makes it easier to get it on. It also allows you to take the head off without needing to heat the vinyl first. Leave it long or else it loses integrity