Were I you I would leave the lower oil pan on and yank the lower drain tube, test it for leaks (Find a pool, lake, pond, ocean, stream, etc. take it swimming, cover one end and see if you can blow bubbles. Repeat from other end.) I'd also replace the grommet and the o rings, and heck go hog wild and replace the paper gasket.
If the grommet comes out intact yippee. If not then I'd chase missing bits by removing the lower oil pan.
I would also carefully evaluate the condition and routing of the block heater and whatever else is now easily accessible, like the cyclone drain tube mount for example....That would about what I wuld do....It would hard to restrain myself not to do more as I have chronic ship fitters disease.
Cheers
