My 2005 Lexus RX330 is leaking transmission fluid from the front differential breather.

My 2005 Lexus RX330 is leaking transmission fluid from the front differential breather. It had recall service (driver-side floor mat and brake master cylinder seal) on 10/29/2011 by a Lexus dealer, and the leak started after that. I found out that the transmission fluid is overloaded (higher than the “hot” level on the dipstick when the engine is cool); and I asked the dealer whether they accidentally added transmission fluid (of course they said “no”). The car had not been serviced by anyone else, including me, related to transmission fluid. And the transmission fluid overload is a total mystery. The Lexus dealer said a seal inside the transmission is the problem and the cost of fixing it is over $2,000. My question is whether the fluid overload is causing the leak from differential breather, and draining out some fluid will fix the leak; or the transmission fluid overload caused the breakdown of a seal inside transmission and the $2,000 work has to be done? Thank you.