I use Autoglym fabric hood cleaner and protector treatments. it comes as a pack for about twenty quid, I recommend it for removing the grey shiny crease marks which in my opinion are caused by a dirty hood being folded up and down repeatedly. I used the treatment this weekend with great results. Be careful to buy the fabric hood cleaner not the vynyl one. It comes with a proper sponge that activates the soap, clean the hood in sections using a circular motion, it foams up nicely, let it soak in for about five mins and spray off with a hose until the water runs clear, You can see the muck coming out. The hood protector treatment is great, makes water stand on the hood in beads and maintains a nice deep black finish. Warnings..... use an old towel to protect the windows and panels from being misted by the proofing treatment, it's a bugger if it gets on the paint and you will need a clay bar to get it off. (I speak from experience) but I enjoy using the clay bar anyway......