1993 cs 100 problems..oil leak but fixed smog

[wpatters1229]

Got a nice 93 CS 100 with all the bells and whistles. In CA to pass smog you will have to replace the catalytic coverters with NOX busters...they do the job. My only problem is that it seems to loose about a couple of tablespoons of oil when it sits. I thought it was the drain plug but I replaced it and the washer and there still seems to be a leak somewhere around the engine.
I was thinking of dumping some sort of oil additive that might seal up a minor leak. Anyone know of something that might make a seal swell up and stop a leak? I have heard that on older cars the gaskets will shrink and start to leak and that adding some chemicals to make them swell actually works an will not hurt the engine or the oil....any truth to that?

Thanks

[wpatters1229]

I found the major oil leak but do not know what this thing is; It is a plug that is at the rear of the right cam/head . When I took off the bracket that holds it in place I just pulled it out with my fingers and it was covering the end of the overhead cam shaft. It has an "O" ring around it that was pretty flat but on further discovery it was like a plastic or fiber material and broke. I put it back on this plug and used some high temp form a gasket and shoved the plug back into the rear of the head. Replaced the braket and the leak has stopped. Is that plug simply a hole to remove the camshaft if it needs to be worked on?
I still have a minor link around the rear bearing of the crankshft but not that bad. This plug thing on the rear of the camshaft was the main one.