Hi,
It's common for the front and rear panels to be made from either self coloured GRP (fibreglass) or acrylic capped ABS plastic mouldings. The van side walls could be either painted aluminium or one of the above plastics.
The self coloured plastics mouldings and painted panels will always be a little different in colour - take a close look at your car if it has "body coloured" bumpers and is a few years old - and make sure you're not confusing this shade difference with surface degradation:
If the van is stored out in the open - or used a lot - then aside from shade differences caused by the different materials - sunlight will degrade the plastic surface.
The way to correct this is to polish the surface, removing the degraded layer, and even though you say you used various polishes I doubt that you have been doing this.
A polish is a material with a cutting agent, like T-Cut (or toothpaste), that is primarily designed to remove microscopic layers from the surface - until the surface is clean and smooth.
A wax is a material that seals the surface, like Turtle Wax, protecting the polished surface.
So buy a bottle of T-Cut, and if you've tried that once - then keep trying three, four or five times until you remove the degraded surface. Then wax with a quality paste wax - it's more effort but lasts longer.
If the surface has really gone to the dogs - then you'll need a more aggressive cutting agent - try a boat chandler because they have loads of specialist stuff for GRP boats.
Robert
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