I heated up the nozzle separately in some boiling water and scraped off almost all of it. Then I put it back into the hot end and heated it up to 200 C, took it back out and q-tipped off a lot of the rest. There's still some but I'm running a print right now and it's working fine.
Mr. President, that man walked in here with a big blue box, and three of his friends. And, that's the man he walked past. One of them is worth listening to.
Use a knife and carefully scrape off what you can while cold. Heat to printing temp and wipe off what you can. Cool down and clean with acetone if need be.
Edit: do this only with metal pieces. Disassemble head if need be.
PLA basically doesn't dissolve in any (readily available consumer-grade) solvents. Your best bet is going to be to take the entire unit as far apart as you can until it is metal only components, heat it with a heatgun to make the PLA soft/melt, and brush it all off with a brass cleaning brush.