At 140,000 miles the front of my SC300 engine seeping oil in the underneath pan and valve covers seeping oil as well. Had the the front seals and timing belt replaced as well as valve covers. After driving home noticed oil seepage around the front cam cover. Researched to discover it was probable the V V T gear/pulley leaking due to rubber o ring failure within the gear as it becomes brittle with age. Took it back advising the mechanic -- they removed the front top cover and discovered I was correct. Although rubber 0 ring replacement documented on youtube, I decided to purchase the gear complete from Toyota as the mechanic reluctant to risk due to Toyota's statement that the gear is "unservicable."
Lesson learned - might as well replace the V V T gear or choose to replace the o ring only when addressing any cam seals, timing belt, water pump etc replacements.
It is a notorius high mileage oil leak issue for V V T 2JZ engines. The gear/pulley assembly is part # 13050-46010 if decided to purchase the whole unit. Otherwise an o-ring that works is availiable on Amazon listed as a V V T 2JZ o-ring replacement. The o-ring not availiable from Toyota as they define the gear as "unserviceable."
There are several instructional videos on Youtube under Lexus GS models. Trust this will save someone an additional hassle diagnosing front end oil leaks.