Advise to spend $200 - $1,000 to repair it for following reason:
1. Environment friendly. A bad exhaust system may equal to 10 - 100 car's exhaust
2. More comfortable
3. Avoid embarassment
It could be just replacing the piston ring, spark plugs, spark plug cables. Get a few quote. Help yourself and the environment.
No need to try the oil addictive. Tried that, it is useless. Using full syntetic oil is useless as well.