What RockBit said.
Most likely it is debris in the needle/seat, especially if it was running fine previously. The debris prevents the needle/seat from being able to close off the fuel supply. The float bowls fill up with fuel, and fuel spurts out of the boosters and the vent tubes if it is really bad.
When you shut it off, it leaks fuel until there is no more fuel pressure in the lines, and guess what? That fuel goes past the rings and into the
oil pan. So, you may want to change the
oil too. Check the
oil, and see if it is reading too high or if it reeks of fuel.
The fix is fairly simple. Remove the needle/seat, clean, and replace with new if you suspect that the seat was damaged.
You should also question how the debris got in the lines in the first place. Was something recently changed in the fuel supply? New hoses? New filters? If nothing changed, where did the debris come from? Is the filter effective? Are the fuel lines old and falling apart?