A couple of months ago I replaced both my fork seals for the MOT, one of them was weeping slightly. I have now noticed the opposite one is  leaking after about 200 miles.  :x  On investigation I found a very very tiny dent on the slider. When I say small I can hardly see it but I can definately feel it. Its not a scratch or the chrome flaking off, more like something hard has come into contact with it and left a slight dent less than the size of a pinhead. This has almost certainly damaged the seal as its on the area of travel . I have rubbed it down with fine wet and dry and will replace the seal again when I get chance. It could have happened after the original seal change or I could have missed it when I did the change but the moral of this story is to check the sliders very very carefully for any imperfection when changing the seals.

Thanks for the heads-up. I'll be changing the fork oil sometime soon.