I have heard a lot about a product Auto RX (www.auto-rx.com) on this site as well and on bobistheoilguy.com . It is supposed to clean all the gunk and it stops the leaks by swelling the seals etc ..

My car is 1990 240 wagon at 209 K miles . I switched straight to mobil-1 four oil changes ago (3x3000). I did put 1/3 sea foam for 400 miles before doing that .Also I changed filter after 1500 miles in the initial change. So far all this has started a very tiny leak which I see at the bottom of bell housing ( I do not know which seal is leaking) . If I clean it the oil makes a drop after 4-5 days . It did not leak at all before that so may be the oil is the culprit. As far as running is concerned I do not see any change . I have used quaker state for the 4th oil change. I do not notice any change in oil consumption which was negligible before change. I do not plan to change OCI as most of the trips I take are small . I am also shifting to cheaper synthetics e.g Quaker State . Shell rotella and supertech ( Walmart brand) etc as others have noticed that they are also good oils .
Regards
Gopesh