Check the reed valve when you replace the gasket and plate.
If it bent/broken/or not sealing, it will pump oil into the carb.
As far as the left side using oil, its probably either a bad head gasket or worn rings.
Keep a few extra sparkplugs around and keep an eye on the oil level.
Fix one problem at a time.
Slappin Pistons Into engine bores is what I do.......