Lacquer thinner....that will dissolve dried acrylic in no time, I swear by it...though it stinks.
Works all the time
Alcohol and soapy water just doesn't do it when the paint is dried and crusted.
As soon as youre done painting, crank up the pressure and flush-flush- flush with alcohol BEFORE it dries ! Then dissasemble and clean thoroughly (still with alcohol, but dont wait till the residue dries).
If you let it dry or residues accumulate due to improper cleaning, then its a job for mister Laquer thinner .
Cheers and happy painting.