Leroy Swann, I'd you have oil coming out of your exhaust, there are 3 possibilities. 1: your head gasket is broken (easiest fix but mostly never the problem). 2: you have a stuck valve and oil is spilling into your combustion chamber. There are two valves on the head of the engine. One let's the fuel into the combustion changer while the other let's out all the gases after the fuel has been ignighted.
If one is stuck closed it is building up way too much pressure which spill oil into the combustion chamber. Oil is hard to ignite and ends up leaking out of the exhaust. ( sometimes the problem) 3 ( most of the time and what happened to mine) in you combustion chamber, thereal is a piston that moves up and down to compress the fuel to ignite it and release gasses to the exaust. On that piston is 5 or 6 rings.
If the rings end up going out oil leaks onto your combustion chamber. What I had to do once I had taken the engine apart is buy a new piston, rings, and a rod. The rod connects to the bottom of the piston to the crankshaft so the piston will move. When the rings go out, it caused the piston rub on the engine wall and take metal off the piston.
Just a thousandth if an inch off will destroy the engine. Since the piston had metal rubbed off, it ran differently and took metal off the rod where it connects to the crankshaft. The piston, rod, and rings, and gasket kit ( GET A GASKET KIT EVERY TIME YOU TAKE APART YOUR ENGINE AND REPLACE THEM) cost me about $150 online.
If you go to sears it costs a lot more. If oil is coming from your exhaust there could be two major internal issues, and one not so bad upper engine repair. The first is piston rings, the second is valve(s). The fairly easy fix is the 'head gasket'. To check these options, you will need a cylinder pressure gauge. Screw it into the sparkplug hole and manually turn the crank until the highest pressure appears.
Then just watch it for a bit. If the pressure falls suddenly, you may want to consult a professional about rebuilding the lower engine. You definitely don't want to run it in that condition, because it could cause even worse problems later. My guess is ring or valve job. Cost depends on what you are comfortable with.
Craftsman Lt 2000 Owners Manual
Good luck, I'll be praying for you and your mower.