Oil can come from different places. If it is not obvious, it may travel down the transmission dipstick from the driver's side valve covers. You may just have to torque the covers back to original specs as they may loosen over the years (do not over-torque).
I had the same issue with Trac light. You can pull the codes by jumpering the ecu plug (search forum for retrieving codes) and if you have trac 43 and abs 54 then I would not assume you must change out parts for big money. I posted this on http://www.clublexus.com/forums/showthread.php?t=322396 concerning the trac system:
Had Trac 43 and ABS 54 codes with TRAC light since purchasing 11 months ago. After referring to many helpful forum threads, a tech manual, and Toyota training documents online, I figured the ABS/Trac/Brake system may not have been bled properly after work on it was performed. Also, I wanted to verify the bubbled hose connecting the accumulator/pump was not a problem since it made no sense that it could be "sucking" air through a slightly weeping high pressure hose.
Using the tech manual to bleed the system, I realized how easy it would be to screw it up. Also, components may look bad just because it was not being bled correctly. After properly bleeding the system, quite a bit of air came out of the TRAC actuator (this is on the right side). The accumulator (on the left side) did not have any air and the fluid was crystal clear even though I had the dreaded bubbled pressure hose.
Here is where I think the bleed procedure could cause a misdiagnosis leading to unnecessary component changes.
The manual says to first bleed the accumulator (on the left side) by starting the engine which they say "allows the Trac pump motor to operate". After looking at other documentation, it seems that there is an SST which is suppose to be hooked up to the pump motor to operate it. Instead of using the SST, it is easy enough to jack up the rear wheels and have someone push on the throttle to engage the pump. This definitely starts the fluid bleeding from the accumulator.
Moving to part two: Bleeding the TRAC actuator (on the right side) by starting the engine which should automatically start the bleeding process upon starting. Initially, I started the car then opened the bleed screw on the actuator which nothing came out. Then I looked again and the manual said to loosen the bleeder plug before starting the engine which did the trick. Air and fluid came out quickly.
The trac system has worked perfectly for a month of everyday driving.
If you are getting a 43/54 trouble code, I would suggest a proper brake fluid flush and bleed (by the book) which includes TRAC/ABS in the proper order. It just may help save changing out components that are still good.