Basement Smell...dampness around sewer pipe

I have had an ongoing battle with my basement. Persistant sewage smell and sewerflies. Connected? I would assume so. I will be selling my home within the next six monthes and need to rid of both soon.
I have discovered dampness and rotted wood etc. near the sewer drain where it enters the basement floor. The pipe is also very rusty. I say dampness because there is not a pool of anykind.
What should i do? Call a plumber? Remove as much rust as possible and "patch" the pipe? (thinking plastic mesh tape and roofing tar)
I need some unbiased advise. Thanks to all that can offer it.

You should have this looked at and evaluated by a plumber. The problem will be found when the house is appraised, and you will have to have it fixed before you can sell it. The bandaid repair job you are considering would be a very temporary fix at best. Most likely it wouldn't even be that good.

That is my first thought to the "band-aid" fix...especially since it appears to be leaking from below ground level or very near to it.