How to dismantle RST 381L forks
I had the same issue and was just about to give up...I don't imagine this is the best way, but it is what worked for me.

Take the bottom covers off.

Take the caps off the top and spraying brake cleaner inside the tube to melt the old elastomers down. I let that sit for a couple hours and then sprayed some Simple Green down in there and let that sit for a couple more hours. Flipped the bike over and tapped (banged on out of frustration) the plastic tubes coming out of the bottom until the springs and old elastomer and all the filth of the last 20 years came out.

Be sure, if you decide to do this, to cover any painted surfaces. You don't want to get brake cleaner on there as it will eat the paint right off.

Good Luck!