I can't seem to get the link to work.
Mike

Mike here is the updated link for images.

https://picasaweb.google.com/vandana.masand/MapleTree?authuser=0amp;feat=directlink

The moss didn't cause the damage. I don't know what did.
The damage is enough to warrant taking it down, before it falls down and does some damage. It has started to heal, but the damage is too great to completely heal over and save the tree.

Maybe something was placed between the two main trunks and removed before you bought your house. The damage could also be caused by stress caused by the weight of the snow in winter. Both main trunks lean out. These two guesses are just guesses, but I hope it helps.
Mike

thanks Mike.

I have asked an arborist to come and visit. Let's see what he suggests.