Has anyone serviced the driveshaft? If it's a 4WD model, there must be 10-12 grease fittings as I think back on it. I'm guessing here ... but if you're not doing your own maintenance, I'm betting the DS is not getting lubricated ... even at a Toyota dealer. It's possible your 4R has never been greased ..... Probably a long shot, but worth mentioning I thought.