I have a nylon rod that I use for such situations. Tap lightly with a hammer.
Anything non-metalic may work - piece of PVC pipe - plastic putty knife - etc.
They just snap in place. You might be able to put a kitchen gripper pad on them and muscle them off.
Or did you mean the top slider screw-in cap? for that...
You need to loosen the top triple tree clamp bolt - BUT NOT THE BOTTOM ONE. That top clamp bolt (when tight) keeps the cap from unscrewing. The bottom clamp is necessary to hold the tube while you unscrew the cap.
You can protect the cap with black plastic tape while you use a 1-3/8" 6-point socket (or wrench) to unscrew the cap from the slider tube. A 35mm socket is also usable.
thank you for a quick reply. yes i did mean the dust cap but information on the top nut will make life easier. - Malc
One more note if you are disassembling the forks to do a proper rebuild.
The first thing you should do after taking off the front wheel, while the forks are still clamped in place, is to loosen (don't remove) the damper screw that goes straight up into the bottom of each fork. The clamped slider tubes & the full tension of the fork spring will help hold the damper tube (inside the fork leg) in place while loosening that screw. It's terribly hard to do that later.
Those threads have a lot more info about my Progressive Fork Springs install and info about a number of other model year forks. You may find some or all of them of interest, even when they are discussing 2003-earlier Damper Tube forks.
Before you do that try cleaning the seals with 35mm film or something similar...that will often dislodge a spec of dirt and stop the leak. Motion Pro sells a tool for this...