Yep, I have seen the oil drains like that and maybe one day I will do that to mine. I alway wonder how much oil is left in there by just sucking out from the dipstick tube. Also that would be 1 less thing cluttering up my tool box (for the pump of course)
On the rear main again, I personally would not worry too much as it does sound like a minor groove. The only alternative here is to scratch the whole thing, return the engine and get another (not fun at all). Now you have to hope the new one is better than the one you had, if not you get to do it yet again
The groove itself is not going to cause issues, only the fact that the sealing surface is smaller diameter than it should be. If the reman company where to machine that surface to remove the groove, you would still be in the same boat (hahaha), the surface area would be reduced but maybe more this time because it was machined past the groove to remove it.
Where did you get the motor? Was it Jasper by chance? They have a pretty good warranty so if you start to have issues they will give you another and pay you some cash for the parts and labor too (had to use that warranty once
).
I would definitely take some emory cloth and go around it if you can (or did you already install the seal?). That may reduce it a bit more and make you feel a bit better about it.