This i think is a real problem; especially if someone (oil delivery man) scratches the plastic and you t cut it out-leaving white/fady stains that get worse if you spill petrol when filling the tank-ME!
Anyway my findings so far for what they are worth; Autoglym bumper gel; cheap, nice intial finishe ie glossy but a bit sticky, and rain quickly ccreates run marks in it-not brilliant.
Armorall interior plastic finish as above
A glaze detailer; pretty decent, came with the pack so not sure if you can get it generally, or the price
BMW 's own bumper/plastic care-works well-lasts longer than autoglym teeny bit more pricey but better imo, and a good compromise.
poor boys bumper and trim restorer; gives a really nice finish-as BMW really -does streak with rain eventually but didnt manage to cover the marks left by the petrol-BMW 's does this reasonably well
PEANUT BUTTER-yes seriously-dirt cheap=tried it once and it seems to work really well BUT only had crunchy and gettign the bits out was a mare; watch this space for a review on how it works properly when i can get some!
yet to try; black wow-expensive but developed by a mini enthusiast apparently and
the stuff that Donna recommends; GTECHNIQ permanent trim restoer-expensive though but comes highly recommended as Donna is a perfectionist!