I was bathing grey and white Lego pieces in just hydrogen peroxide and sunlight (outside) in 2005/2006. It took a few hours and worked very well but definitely needed something to speed it up.

The Lego pieces don't seem to have been affected since doing this after just checking the model.

I have used Brasso (liquid) or jeweller's rouge on bricks with fine scratches (build a wall and do a side at a time) to a least get finer lines in the same direction.

Probably mentioned many times before, you need to mention to the retailer:
The machine is not of satisfactory quality so not fit for the purpose it has been sold for.
The lid on a laptop is designed to be opened and closed but doing this has resulted in the lid cracking within 5 months of use on this laptop.
The Item should be replaced, repaired (by the manufacturer) or even a full refund given at the retailers discretion within the warranty period.
As it is a manufacturing problem you can even get it fixed outside of warranty (had same problem cracked lid 2 months out of warranty on a laptop)
See: http://www.tradingstandards.gov.uk/cgi-bin/calitem.cgi?file=ADV0043-1011.txt
UK trading is very pro consumer, in some cases too much.