One problem related to power train driveline has been reported for the 1999 Toyota 4Runner. The most recently reported issues are listed below.
Frame on 1999 Toyota 4runner has rusted through in front of rear axle attachment on driver's and passenger's sides. Rear differential cover has also rusted to point where differential fluid is leaking out. The vehicle is well maintained and washed regularly with no rust anywhere but frame and rear differential. The vehicle is unsafe to drive and must be repaired according to mechanic. Toyota states that they have a voluntary buy-back program on tacoma's of same vintage, but not for the 4runner?.