Please excuse the long winded post, but I'm looking for some advice, and I want to be sure I don't forget any facts.

A little over a year ago I purchased a new 2007 F150, with the 4.2L V6 & 5 speed manual transmission.
About 3 months after I purchased it I noticed that the clutch pedal linkage started to make a dry squeaking noise. It sounded like it was coming from where the linkage rod goes through the firewall.
At the first service (Jan. 2008, 2400 miles), the dealer removed the transmission, lubed the throwout bearing & clutch flex plate, and reinstalled the transmission.
That quieted the linkage for a couple of weeks, but the sound came back.
It progressively got more noticeable, and the clutch pedal began to occasionally get sticky & gritty feeling when being released.
I took it back to the dealer in June (5300 miles), they replaced the clutch slave cylinder. In their report it states that they could feel the stickiness in the old slave cylinder after it was removed. This eliminated the squeaking and stickiness.
The last couple of weeks I have noticed that the dry squeaking sound is beginning to return. And I'm concerned that the it will get progressively worse and the sticky/gritty feeling will return.

Has anyone else experienced this with their late model F150?
Is there anything else the the dealer should be looking at? I say dealer because the truck is under warranty for another 5 years.
Is there any way to lubricate this area of the clutch linkage?

Any advice would be greatly appreciated.
Thank you,
Tim