I would definitely change it from under the hood. Just looks like 4 or 5 bolts, an electrical connector and what looks like a drain hose...

http://www.autozone.com/servlet/UiBr...3d8015e861.jsp

Yup, I can change these out in under 5 minutes -even in the dead of winter -did on my mom'* old 1988 Olds Regency Brougham (the 3800 that started it all for my family -our first taste of a 300k 3800). Also did it on my moms old 1992 Park Ultra, but that was in the summer so it was a piece of cake. Have also removed a few -heck it'* still easier than W-bodies where you have to remove the lower dash panels and lay upside down on the seat like Jason said.