I know this is an old thread, but I just noticed it. My 1991 Accord (recently sold) started erratic lock-up behavior at around 300k miles. It was worse in the winter. After doing a series of 4or 5 ATF drain-and-fills over almost 2 years, using the Valvoline "high mileage" Dex/Merc fluid from Advance Auto, the transmission gradually returned to normal and stayed that way for several years until I sold it this year at 416k miles. - Joe