repalce crankshaft seal. if shaft is worn will replacing the seal be sufficient to cure the seal leak
Maybe. But it won't last for long before it starts to leak again.
If crank is worn theres no point in doing the seal but if its a straitforward oil seal the crank should be ok, oil seals usually harden and leak with age
Could be leaking due to pressure in the sump, check the breather system.
