A while ago I hit a stump with my lawnmower and bent the crankshaft in my lawnmower. I could only pull the bottom of the crankcase off partway, so I had to cut the crankshaft in half. When I was doing that I accidentally scraped up the mating surfaces a bit, and of course the replacement paper gasket only works if the surfaces are perfectly smooth, and now it spits oil on either side when it runs. My question is if I can use RTV sealant or some similar method to completely seal it.
Do not use RTV sealant, it is not suitable and you will end up at best with a leaking engine, at worst if it gets the internals, another repair job.
You can get proper gasket sealants that are oil and petrol resistant e.g Hermatite Gasket Sealant. Any decent mechanic will frown upon it's use, but for a lawn mower it should be fine. Just be sparing in it's use, if you have wodges of it oozing out from the joint, you have over-applied it.
You may still need the paper gasket in there too to maintain the correct clearances and use the gasket gunk to stop the scraped up bits leaking.