I have a 2005 4runer. At 10 years old (150,000 miles) I tried a synthetic oil and got many "drips" around the oil pan (and above). I switched back to conventional (NAPA 10W - 30) and the drips slowed down to about two drips every month.
I will not use synthetic oil in my 4 runner ever again.
Scotty Kilmer says it can cause problems in older engines. Watch the whole video.
scotty kilmer on synthetic oil leaks in older cars - Bing video