Bought a excellent quality and expensive 4 year old leather armchair which has been fine for the last two months, but now it's almost as though the padding in the middle of the seat pat has melted away and it feels like spring and then leather on top with nothing to pad. The edges and everywhere else is fine but the main seat is so uncomfortable. Any ideas what could have caused this as the foam has been there for two months and now it's as if it's just disappeared!