This sounds like exactly what happened with the water pump situation.The 2000 Northstars did have casting problems that led to porous blocks. Mine was one of them! At around 44,000 miles I started smelling coolant. I took it to the dealer, and they replaced the water pump. After that, I kept smelling coolant, and they said that coolant was leaking through the block in the intake valley. So who knows if the water pump was leaking or, they just replaced it just in case??? So a new 2002 engine was installed. But luckily for me Cadillac paid for it!
By now though, I would think that all the engines that had porous blocks from that year would have been replaced.
The coolant smell never completely went away.
Car was never overheated. Temperature was not an issue, coolant on the driveway was though.