My bonnet stripes weren't in the best condition when I got it, think the dealer had used some bad acidic car wash stuff that had damaged them. So I had to polish them quite a bit with Autoglym Super Resin Polish then i've waxed them with Autoglym HD wax which seems to have brought them back up quite well.
But I did have quite a bit of black coming off while polishing but I thought well i'm going to need some new stripes anyway if they don't come up well enough.
I have used a machine polisher on mine, with a soft pad and a fine polish. They came up a treat. But they are an absolute pain in the neck to keep black. They smear at the slightest hint of detailer etc.
Such a nightmare to my OCD that I didn't spec them on the JCW.....
I've just decided to replace mine for the reason of the detailing marks. Came off really easily with mild heat applied and then purchased new ones from a decal online (£35 for 2 stripes) and were really easy to reapply. Worth doing as really brought up the car and loads of different styles away from OEM - highly recommend than trying to buff up.
I ended up having mine painted! [the red only]. Removing the old stripes [2018!] left a mess... It was either repainting the whole hood or this... And now my quote is:
"When a bit more becomes too much"... ah!ah!ah!... Ticket magnet at 304 hp...