I have coolant dripping off the passenger side of the outside of the bell housing. The front head coolant cross tube began leaking a few months ago and I replaced the little o-rings that fit down into the recess in the heads. It may be time to replace those same little o-rings on the rear of the heads, but it isn't wet to the touch back there. What else may be leaking coolant from the passenger side below or behind the rear, #8 cylinder? Could it be anything other than that little rear o-ring in the head, or a head gasket?

 

Assuming it is a 5.3, there is a freeze plug also on the back of each head. Check the heater hose connectors at the firewall