Without being too anal about it, I would like to spruce up the engine bay on my 156 GTA a bit. I've got the general interior looking better, but the intake plenum and covers are stained. I've tried various degreasers and good hard scrubbing with a stiff brush with various metal polishes but I can't shift the staining. Anyone got any suggestions? Is this a specialist job?

Cheers,

Nigel