Any advice thanks...

couple of favourites i have for grey..in no order,

blackfire midnight sun
p21s(not very durable)
ADS obsidian.

Ganger said:

Any advice thanks...

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I'd use Armour all Shield "Better than a Wax"
I use it on my cars, It can be applied on plastics, glass and paint without doing anything iffy. Plastics look black instead of gray/white as with other waxes. Great beading, Easy on and easy off if you use a microfiber towel/cloth to apply and buff off.

Link:
http://www.halfords.com/motoring/cleaning-products/polish-wax/armor-all-shield-wax-500ml
Comes with a microfiber cloth

Ganger said:

Any advice thanks...

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You'd be better off with a sealant on grey.

Zaino Z2............