While you had the oil pan off did you swapo the rear main too?? Just curious. Might as well do it when you're down there. It will need to be replaced to help slow the oil leaks. Mind you, it won't stop leaking- the Buick that is. You could seal the whole car in RTV and it would still leak
I didn't see anyone suggest this butjudging by the grimy appearance of the block, and your apparent comfort with removing and replacing the timing chain (some aren't as gung ho), you may want to consider taking some time to just clean everything you can get your hands on. Remove plugs, clean the connections and make sure everything is secure.
If that sensor fell of and hit you in the face, you can probably rest assured that there may be a few other connections that are not as secure as they should be.
Don't be in too big a rush. These cars are a PITA and you will spend lots of time under the hood however, they are addictive
. Make sure you get all the basics lined out before you go crazy modding. Once the car is running well, then you can play. Otherwise, you'll never get the car to cooperate no matter how much money your throw at it and you'll hate it and want to get rid of it...
Oh yeah, welcome to the Darkside.