Planning the next
AO Silver Member
Join Date: May 2007
Location: United Kingdom
It won't do anything for the scratches, but you can get them back to black easily and cheaply. Get some 'Groundnut Oil' from your local supermarket. It's only a pound or two. Apply very sparingly to the grey/black plastic. It will then look black. The nice thing about groundnut oil is that it dries and doesn't feel greasy.
You can also use it on the black bases of the bumpers, scuttle panel etc.
One word of caution, if you do decide to later paint the sill covers, make sure all the groundnut oil comes off first!
The more expensive solution is called 'Aerospace 303'. It's used on yachts and microlight aircraft, it also does great things for faded plastic.
I don't use the groundnut oil anymore as I had my bumpers painted and I got some secondhand phase 2 sill covers and they were refreshed at the same time.