You can use ALCOHOL KETONATUS 90% for this.t solves all the sticky rubber coating but not the thick rubber woofer ring.
Afterwards you can respray it with BLACK PLASTIDIP.
Another option is to buy a vinyl black sticker circle in the correct diameter. Place it over the ugly/damaged/sticky part and you’re done. Those stickers can be made by any local print/sticker design shop.
I see some B&O second life dealers use this ‘secret’ method 😉