What should I beware of when removing this cover? I have a leak back there and have never had one off. Do I need special tools to remove pulley? Cant spell harmonic balancer:doh:

Just unbolt the balancer pull off by hand... Then unbolt the cover and remove... Just becareful not to bend the cover if prying to it get lose... Might be better to loosen with a putty knife. http://mopar.mopar1973man.com/cummins/general/kdp/kdp.htm

Is the leak between the cover and gear case or the gear case to block?

It is between the cover and the gear case, it has a lot of grime there and then it's real clean back to the gear case and block.

OK then go with what Mike posted.