being a bit of a redneck, I have done this repair before without even lapping in the valve, used the valve to hold the seat in nice and firm and just peened it as pictured.

I cannot reccomend my repair methods due to the nature of them, but for older equipment if tools and time is not available I just use what I can.

As for the oily patch, I would not be that concerned, maybe the rings are leaking a little, but just keep an eye on the oil level and she'll be right smile