Don't add "leak fixers". Your tranny has a lot of very small orafices that must work properly. If a "leak stop" stops a small leak then it will stop the oriface that is supposed to be there.
Either drain the fluid and fill it properly to make sure your tranny is not overfilled. Could you have overfilled it???
or find the leak and fix it. If its the oil pan gasket then replace it and while your at it change the filter, since you'll have the oil pan off anyway.
It could also be a seal around the modulator valve or any other seal. Have it taken care of correctly. Trying to "rig" a fix can wound up becoming a very expensive transmission overhaul.
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car