If you do a search on this site you will find a lot of discussion on this topic.
Believe it or not a lot of members recommend using peanut butter! (It is the oil). Also, there are after market products that will help, such as I believe it is called Black Chrome (?) or something similar. It is to restore discolored plastic pieces. Often, several applications are required with vigorous rubbing to get the heavy layer of old plastic off.
I have used the Black Chrome (?) with good success.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)