2012 500 HO leaking fluid

I have a 2012 sportsman 500 HO that is leaking fluid from the front end of the machine. I am pretty sure it is the front gear case. My question is does that just mean that I cannot use the 4 wheel drive feature? Will it still run and function properly or is this something that needs to be fixed ASAP? Any idea what causes this or how to fix it?