if it is supposed to have a gasket then it does need one, yes when the oil thins with temperature it can seep through the threads.
No. It would cause the coolant and oil to mix and it would look like a Milkshake drain oild and check it.
Could be the leak is coming from higher up like a pan gasket or rocker cover gasket, and collecting on the drain plug. Bad drain plug gaskets usually leak continuously whether the engine is running or not.
Yes it would. As well as white smoke, Oil/coolant consumption, And think "milkshake" like oil when you drain it.
Yes, I blown head gasket will definitely effect the emissions.
cause
sounds like it might be head gasket or intake gasket
No. A bad head gasket would cause water to come out the tailpipe. You will see white smoke. Leaky rings would cause oil to come out the tailpipe. You will see blue smoke.
Yes a clogged VENT pipe can cause a sluggish drain
A blown head gasket.
most probable cause would be over heating
Overheating.
most likely cause will be a vacuum leak at the carby or inlet manifold gasket. it will need a new gasket. hope you find a reputable mechanic, it shouldn't cost more than $100 if it is the manifold gasket but the carby gasket could become very expensive.a secondhand carby would be the cheaper option. answer don't go for second hand carb, u may have same problem. make sure choke and choke operating diaphragm is working correctly