I came across this article on engine oil. It clears up a bunch of stuff I only kind of understood. It's pretty detailed, but still in plain english.
FerrariChat.com - FAQ: Motor Oil Articles by Dr. Ali E. Haas (AEHaas)
The summary is run the lightest synthetic you can while still maintaining acceptable oil pressure(you'll need a pressure gauge for this). It probably doesn't apply to preventing leaks though.
It also sounds like the best style block heater would be the oil pan magnet kind since the oil takes much longer to heat up than the coolant.