Found this on another website a while back ... maybe this will help you
The problem is.... That the Nubuck leather gets greasy and compacted, so that it looks like waxed leather instead of suede.
So the first job is to de-grease and clean the leather. There are several preparations on the market for cleaning suede shoes, carpet and upholstery shampoo sprays seems to work just as well. Follow the instructions on the tin. DO NOT USE soap or convetional leather cleaners - they will make the problem worse.
My favourite cleaner is 'Kiwi' suede and nubuck spray.
As the suede dries, keep working on the nap to raise the pile. Basically you will need to 'rub it up' with something abrasive.
In ascending order of brutality, you can use a hush-puppy brush (copper bristles), or a suede brush (nylon bristles or webbing), pummice stone, or even aluminum oxide paper. Whatever method you use, use a vacuum to remove all the loose bits as you rub them off, and finish off with a proper suede brush to make all the area worked on look the same as the rest of the suede.
If you then retreat with a cleaner incorporating a protective substance (like ScotchGuard) it may help to conserve the work you have done.