Faulty mattress claim refused

We have a sealy Ronan mattress that starte leaking/oozing a fine viscous oily substance about 3 moths ago. Its colourless and (mostly) odourless and does not stain the mattress. It does however keep seeping into/onto the bedsheets in the corners. Mostly the bottom part first that then increases over the entire corner over a few day period.

It was reported and an inspector came to assess it. He reported back to the head-office that 'he did not find any signs of it' after I showed him this myself and providing photos. The fact that it does not create a stain (as it is colourless), they say, shows there is nothing wrong.

Some slight researching on the subject show results that it could be from material breakdown of the foam used or some of the fire retardant materials used within the mattress - this being a health hazard too by the way.... They deny this and deny any claims.