If these are showing flow lines in the plastic moulding this is the cumulative effect of daylight/UV exposure which has gradually exhausted the antioxidants etc in the plastic compound. As @lunchbeers suggests this can be remedied by the judicious application of heat (there are various YouTubes showing this - especially for stadium seating). What this does is migrates more of the antioxidant/pigment package to the surface but the problem will return and probably more quickly.
I have and do use this but it is a poor fix because it fades quite quickly. The immediate effect is however excellent. Life span is around a month in my experience. Armorall Shield seems to work the longest. The effect fades but I get 6 moths looking reasonable / good. The ease of application is easy too. It doesnt matter if you get it on lkight coloured paint it polished off. The only reason I dont use it on everything is rain marks can form where it is subject to drainage runoff and these then have to be repolished. On white paint its a nuisance.
On mine I usually find it being ok for about 2-3 months before needing to be done again but then again when I do the weekly clean I go over the entire car, trim included with my 50/50 mixture of Turtle Wax black spray wax & Sonax BSD & then on top of that at this time of year with the pollen etc I have a 50/50 mix of Megiuars Ultimate detailer & Chemical guys Speed Wipe which is helping to stop the pollen sticking to the paint, good thing is because the cars black & I hand polish it every month I just go over the trim with the black polish whilst doing the rest of the car & it comes back up
makes my life just that little easier 
I have used this stuff in the past but found whilst it brought it up really good when it rains after applying it & even buffing it off, on black paint it would leave noticeable streaks under the trim on the panel, I don't like the stuff that makes it all shiny & glossy, I much prefer the matt finish look myself, I purchased G Techniq C4 a little while back, whilst it good mine to look semi good the finish didn't last long before fading again, was about 3 weeks, but on my dad's Punto I did the plastic scuttle panel & the first bit of rain it's left permanent white water spots so I wouldn't recommend it & near on £40 down the drain
www.owatroldirect.co.uk
With a black car that concoction sounds good. If your using the black polish then doing the plastic as well is entirely logical. I just did my white one with Autoglym Gold sealant On top of my original caramic coat it does a good job, but NOT on black plastic.On mine I usually find it being ok for about 2-3 months before needing to be done again but then again when I do the weekly clean I go over the entire car, trim included with my 50/50 mixture of Turtle Wax black spray wax & Sonax BSD & then on top of that at this time of year with the pollen etc I have a 50/50 mix of Megiuars Ultimate detailer & Chemical guys Speed Wipe which is helping to stop the pollen sticking to the paint, good thing is because the cars black & I hand polish it every month I just go over the trim with the black polish whilst doing the rest of the car & it comes back up
I've got a few concoctions to keeping the black paint decent using the tried & tested "trial & error" method
& have my own little routine with it
This is probably the best trim restorer I've used last a long time 6 months + and still haha good finishYou could try this stuff - did work really well on the stone chip protectors on my Cinquecento Sporting.
Polytrol | Colour restorer for faded surfaces | Owatrol Direct
Restore the colour of faded surfaces - great for car bumpers, boat gelcoats, tarnished metals, faded stone, tiles, paint, plastics and fibreglass (GRP).
