It is likely the float valve is not seating properly. Needs cleaning or replacement.
It depends on why it is leaking.
it depends on where its coming from
Depends on where it is leaking.
oil leaking on the ex man fold need to fix the oil leaks
Your gas tank or one of your fuel lines is most likely leaking and your rear differential is probably leaking also. Your head gasket is located in the engine which is in the front of the car, not the rear. Take it to a mechanic because you DO NOT sound mechanically inclined enough to fix anything safely.
If the oil sending unit is leaking oil by the inside of the component, then I don't know of any way to fix that other than removal and replace with another one. If it is leaking by the threads, then you can try teflon tape to seal that. Also make sure it is leaking from the sending unit and not leaking down from the valve cover.
It is not totally unusual. It should not happen though. It means that your carburetor is leaking gas through while the mower is not running. It will fill the cylinder and get into the oil. A quick fix is to get an inline gas shutoff valve and just shut off the gas when you are not using the mower. Otherwise you will need to rebuild the carburetor to fix the problem. You will also have to clear out all the gas from the cylinder and if it got into the oil you will need to drain and change the oil.
antifreeze leaking into the oil pan
tape
check your pinion seal
the reasons I can think of right off are, a bad mechanical fuel pump( in which the diaphragm is leaking and gas is running into the oil) or an engine that had flooded during start, or leaking rings which is letting gas run by the pistons into the oil. (last case engine is pretty much worn out)
the only true way repair the leaking oil pan it to remove the pan and change the gasket their is no quick fix for a leaking oil pan if you do it right the first time it wont bie you in the but latter