99 RX300, FWD 162K. Trans fluid never changed, until clogged screen caused Whine at startup, and not engaging - slipping. Changed filter and 4 qts T-4 fluid; 2 hours - it works shifts fine, whine gone (insuf fluid circulation)! Didn't do as much as Foster - purging. Seems clogged filter - totally blocked - is major element to failure. Will keep tabs, and do purge if problem recurs. Thanks to all DIY and Pros who posted. $50 fix!