96 F150 4X4 5 Speed Leaking Slave Cylinder

A caller (Mike 3/27/10) was complaining about his slave cylinder leaking on his clutch, Tom & Ray offered that it could be (seal) ‘shrinkage’ and suggested he replace his clutch master cylinder. The problem I have with this answer is, a leaking master cylinder would not account for the loss of fluid and the caller did state he had to refill his reservoir. I have the same model truck and have experienced this very problem (repeatedly). I have found the slave cylinder piston seals wear out. On average mine seem to last about 18 months. Shrinkage comes into play when it’s worn and cold (temps around 32 deg F). Last week I installed slave cylinder #6 in 10 years. On #4, I replaced the entire assembly Master, line and slave and still only got about 12 to 18 months out of it. I have not been able to determine what, other than poor quality control in the manufacturing process, could be causing what I and many consider premature slave cylinder seal failure. Any discussion, suggestions or musings are welcome. I had been using Prestone DOT 3 Synthetic and have just opted to use Ford’s brand of fluid to see if that helps. Contamination is not suspected as the reservoir is on the firewall, away from all other fluid fill points. My cap seals tight, has a good seal and stays clean. I don’t open the reservoir, other than the occasional check, until leakage begins to affect operation of the clutch.

Good question.
Since it’s inception as a F2TZ-7A564-A in 1993, the part number has undergone NINE number changes.
With o.e. parts , number changes occur when something about the item has changed at the production level.
In the past 12 months we’ve sold an average of 6 per month.
Years ago I can remember selling a dozen a week.

If you’ve bought part# 6L5Z-7A508-AB most recently it should be lasting a lot longer.

But your questions still remain unanswered as to why this lack of longevity has never been perceived as a problem or ever been recalled, only addressed by production changes.
The changes they’ve gone through are making a big difference. Dealer o.e. parts are warranteed for 12 months/12,000 miles even if d.i.y.