I've been leaking small amounts of dex-cool by the bell housing underneath.

This is more than likely the heater control valve. They are not fun to get to, but easy to diagnose. This is really a large job, and if you are not completely confident I would recommend one of the shops under the link below: http://repairpal.com/cadillac-within-10-miles-of-fairmont-west-virginia-26554

Mine started leaking over time got worse. I removed the plastic covering by the windshield wipers to gain a little more access was able to remove the old one no problem. I replaced it with a simple T fitting for a sprinkler system 3/4 inch if I'm not mistaken. Then pinched off the vaccucm line to the old valve. $1.75 for the fitting and full heat and hasn't caused anymore problems in the year is been on there. Id say skill level 4 out of 10