I normally use T-Cut to polish both the lacquer and plastic grips of the Carene but wanted to give a dedicated plastic polish a try.
I purchased a 5g tube of polyWatch which is a watch crystal plastic polish. It is not cheap at £4 a tube but very little is required to provide a nice finish.
Using an old section (waiting for a new nib)
small dab of paste and a few minutes rubbing with a cotton bud,
an acceptable refinish,