Gaynor from Paraparaumu says she has read it may in fact make stains worse, and instead suggests baking soda and vinegar as a cheap and non-toxic cleaning agent for brass, silver, gold, bronze, enamel, stainless steel. Also toilets, glass, fibre glass and oil on concrete.
[We have had a quick look at the WD40 website and it does recommend it for a number of cleaning purposes. However, baking soda and vinegar would be cheaper. – Oily Rag Ed’]