Like many others, I've experienced difficult shifting problems on my MT 5 speed 2003 Accord LX. Out of habit, I first replaced the slave cylinder, with only moderate (and temporary) improvement. I then replaced the master cylinder, (using all OEM parts, for both slave and master), but here's the question: The Service Manual mentions replacement of an O- ring on the clutch line, which appears to be the same as a rubber washer inside the master cylinder unit itself. I asked the question of the parts guy at Honda Dealer, and he seemed to thing the O-ring was already inside the unit. When I pulled the original master cylinder, the rubber O-Ring (which is really more like a rubber, flat washer, as mentioned) insider the unit was intact, and I did not see any sign of an old O-ring that may have been part of the line itelf (unless it either fell off during removal, or disintegrated over time). There was a a lot of dark fluid bleeding out from the slave cylinder when I had replaced that unit.

Does anyone know if a separate O-ring (separate from the rubber washer inside the master cylinder unit) is indeed added to the clutch line? When I re-assembled everything (without the added, questionable O-ring), the unit did not work properly. I found no line leaks, I could bleed down the system OK, but could not get the slave to work properly.