Hmm...the surface treatment right at the base has deteriorated.The edges became roughened and  matte in places,just like the metal in it's natural state,if you look at the inside.We were told that it would be repolished.When it came back the standard of workmanship looked very amateur.A month or so later,the original problem   has started to reappeared.Now the dealer says the complete base was replaced and they will come over to polish it up [again??] The unit just sits on a wooden chest.We have been told two different stories and want to sort it once and for all.

Polishing the base will be futile. The aluminium has been anodised and will be impossible to restore to it's original condition by polishing, in fact it will probably make the situation worse as it will remove even more of the anodised layer.

Is the unit still under warranty? If yes then you should insist that the base is replaced by the dealer.

I agree with Graham, get the dealer to replace it even if it is not under warranty, you should not have those problems with a deteriorated surface.