FLATLINE:
First of all, WHAT kind of aftermarket fork do you have? Pro Circuit SHOWA kit?......... KYB kit?.............. Greeves leading link? This is vital information to know how to help you.
If you have a late style "twin chamber" fork like the SHOWA kit or KYB kit, then you need some special tools. The main spring is located in the bottom of the fork, not the top like the earlier models. An easy way to tell is if the top fork cap has a very large outside hex construction with a smaller, "inner" cap. To get the cartridge and spring out, you must unscrew the large outside hex (you will need the correct tool) from the outer tube, then this will allow you to compress the outer tube and inner tube exposing the top of the cartridge. YOu can drain the oil from the inside by turning it upside down and allowing the oil to drain out. Next, secure the axle bracket in a vise, and loosen the bolt (either an allen hex or bolt head) until it spins freely and you can feel the threads are all the way out. NExt, compress the top of the fork cartridge into the outer/inner tubes, and the bottom bolt should extend out against spring tension. There is a special tool for holding the bottom bolt extended out, which is a flat plate with a notch cut out of it. This allows you to remove the bottom bolt from the piston rod by loosening the jam nut. Now you can remove the cartridge and piston rod from the fork, and change the fork seals.....
MOP...