Rob,
Probably a bit late to be any help as others have covered this, but are you sure you were on the path when you found it so disgusting. The first time I did this I strayed onto an argocat track which is, indeed, pretty horrible. I am also aware of a couple of challengers, names withheld, who made the same mistake and had a hard time getting back down again. The path on the map is actually quite nice and well defined - there are many worse.

If you are heading for Dalwhinnie it is easier not to cross where shown on the map - carry on until about NN468725 where the water splits (divide and conquer) - this is shown on an Explorer map but not Landranger.

Colin.

Thanks Colin. I have marked that GR on my map!