Replacing the seals
Starting point

Remove Cap bold

After opening, remaining oil will drain a bid.

Use a strap to compress the spring a bid to get room for the spanner

Turn the Cap lose

Remove the cap and spring

Remove dust seal carefully with a screw driver
Make sure you don't scratch the inner tube.

Remove inner spring

With some hard pulses pull the outside tube from inner tube.
This can be rough work as they may get stuck quit heavily.

(don't hesitate as you have to do 10 till 15 hard pulls)

Here you have a situation layout

Remove the DU bush by opening it with a screwdriver

Make all parts clean

Placing the oil seal.
Use some isolation tape, to make the seal glide easier over the trouble zone.

After that, grease the DU bushes a bid.

Take the time to press the DU bush into its place.
Pull the outer tube almost to its Max position, to prevent any scratches/dens (on the inner tube) when tapping the bush in.

Tap on the Washer, not on the DU bush.

Press the seal gently in to its place then mount the seal spring

Last, press the dust seal on its place