WD40 and time! I sprayed the forks on a couple of Arcos I had that were nearly stuck, I sprayed them daily for a week then took them off and put them in a vice with padding so as not to scrape the forks. I used a propane torch and carefully heated the tubes not the springs and with a crecent wrench carefully turned the lowers a little at a time and they slowly came free. I twisted them and guided the springs out of the pockets then cleaned the fork tubes with a wire brush, and the inside of the lowers with a plumbers brush and more wd40. When all was clean and rinsed I painted everything and just put some axle grease on the tubes and inside the lowers, they work great now! Good luck!