If you remove the pressure release valve at the back of the body, the filter should be inside the chamber that runs the length of the body. it a long thin mesh tube.
If you have a Ds board then its more than likley that its an older shocker and may not have one (depends upon who had it from new and if they fitted one), so it would be worth checking to see and if not put one in. I think they are about £10 or so for a filter.
The solinoids i think are about £60 to £80 to replace depending on which ones gone.
so for the sake of £10 is well worth it
cheers
Bruce