I've been using Surf City's Black Max on my panniers top box, and other plastic bits. It does a good job and is non greasy unlike Armor All which attracts dust. However it is expensive at $25.00 to $30.00 Au for 273 ml. I was in Aldi this morning and they were selling Power Force Protectant 500ml for $5.00 Au a bottle. So I bought 2 bottles which should last me at least a year plus. I gave it a try when I got home and it shined up the plastic with little effort and is non greasy. The Surf City protectant did wash of and needed to be reapplied every couple of weeks. The Power Force looks like it will also wash off with water. The only trouble with Aldi is their products go on a cycle so you have to wait 6-12 months for it to become available. For the price it's worth giving it a go.

Regards Martin.

Sounds odd but Lemon Pledge for furniture also works pretty well on plastics.  I use it on my non-leather seats and it also does well on helmet shields.

Lemon Pledge works best but I usually use non-lemon versions of Pledge since I'm somewhat allergic to bee stings and the lemon version tends to attract bees when stopped.

(learned about this over on ADVrider many moons ago)

Another plastic protectant that has a very good rep is 303 which I also use.

I'm pretty sure we used to get Lemon Pledge in OZ years ago but alas no longer available I have seen it suggested before. I have tried 303 and it is available and 296ml is about $18.00 but I preferred the Surf City protectant.
Regards Martin.