The USD forks on my mk2 seem to 'stick' through the first 1/3 of their compression. The bottom part of the stroke is nice and free and progressive. The top part of the stroke feels very sticky and doesn't seem to slide freely. The forks have had new bushes, seals and oil; non of which made a difference. With the spindle and locking nuts slightly loose the problem persists, so I am confident the forks aren't being pulled too far in As suggested was suggested to me. Anyone have any ideas what to try next please? No real way to tell if they have any slight damage on the legs without sending to a specialist.

(I think they are actually early 90's vintage CR 250 if that makes any difference).

You're going to have to take them of the bike and test individually.
Dropping the oil and spring out will let you feel what's actually going on.
Put the longest straight edge along the length of the fork that you can, and look for any clearance between the straight edge and the stanchion along the length of the straight edge, use a feeler gauge, test at 90deg all around the shafts.
Mike

try taking the legs out and rolling them on the edge of a flat work top with to bottoms over the edge
you can then use a steel rule to measure any run out.
if they are good you may need to take them apart and see if anything has come adrift.