The trim around most of the doors gets very encrusted over the years and various methods of cleaning it have been proposed. This is just one that is a combination of those ideas using a cheap and available product that isn't too corrosive - White Spirit.

Other suggestions were petrol and nail polish remover (acetone)

Rubber trim before

Rubber trim after

Before starting, you will ideally need a strong pair of rubber gloves, some white spirit, a rough cloth like an old flannel or cut up towel, a small scraper and plenty of elbow grease!

Pour a little white spirit onto the cloth and gentle run it round the trim. Where there are crusty parts,  gently run the back of the scraper over it to crack and loosen it and go over again with the cloth to re-soak the whole trim lightly. Don’t apply pressure near any of the corners as the trim tries to pop out at the slightest excuse!

With a clean part of the cloth, a little more white spirit and a lot of elbow grease, concentrate on sideways rubbing of short sections of the trim until clean. The crusty areas will come back to a good state with a few more gentle wipes of the back of the scraper to break the bond of the gunge!

When all complete, wash with a little detergent and plenty of water, using an old toothbrush to get into the crevices! When washing and waxing in future go round and give the trims an extra wipe as the wax appears to congeal on the rubber!

Hope that helps but if any of you find a cheaper or better solution please get in touch.