Burn marks on the back?

Well one things for sure,it's not a leakage of coolant else the fridge would have stopped working when the the cooling circuit lost pressure.
It is highly likely something has been spilt and it has dripped down the back onto the cooling radiator fins(which get warm) and what you are seeing is the residue. Liquid soap or other cleaner perhaps?
With regard to the burn marks these are a bit of a mystery. They did not come from the normal operation of the fridge. The outlet connection of the coolant compressor does get hot and it is always possible that some paper or other burnable material has fallen down the back of the fridge and eventually smouldered and burnt itself out leaving the burn marks, but this is extreemly unlikely.
What is highly possible is an accumulation of dust hair and airborn debris has formed a layer underneath and round the back of a fridge. This material can burn and flame will travel wherever the layer is thick enough. These types of fires are very short lived and commonly leave a series of scorch marks This may explain why you seem to have three burn marks.
Anyone dropped a match recently?

Cledlyn
July 2008