Ford Ranger 2000 4x4 clutch transmission problem

I would think that this was a really rare problem, except that my wife's Explorer had the exact same problem last year.
The truck is a 2000 Ford Ranger 4x4 with a 3.0L engine and a 5 speed
manual transmission. Total mileage: 155,000. Otherwise the truck is in great shape with no history of serious repairs.
The problem: Yesterday the truck started making a scraping sound when the clutch pedal was depressed. It was especially noticeable when slowing down and downshifting. The noise appeared to get worse as I downshifted from higher to lower gears. The clutch was still working fine.
Later in the day there were times when it was nearly impossible to shift gears. The nose got worse and I didn't think that the truck was going to make it home. It appeared that despite the clutch petal being fully depressed to the floor that the clutch was not totally disengaging.
Then the noise spontaneously went away and I could shift the transmission again. It shifted fine this morning too.
As I said, this would seem really odd except that it happened to my wife's 2000 Ford Explorer last year. Over a period of months the noise would come and go and it was hard to shift a few times. After we put some fluid in the clutch master cylinder reservoir the noise and the shifting problems went away and have not returned.
In my wife's case, our local mechanic didn't have a clue was to what was making the scraping noise. It was not the clutch "chatter" that we all have experienced at one time or another. And the clutch in both vehicles has never shown any symptoms such as slipping.
Does anyone have any idea as to what this problem could be and how to resolve it?
Thanks
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Multiple problems:
Clutch hydraulic system, clutch release bearing, probably also worn clutch disc and pressure plate, flywheel resurfacing.
In other words, it has served you well, now you need a clutch rebuild job.
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wrote:

slave cylinder. I have never gotten that many miles out of a clutch before. I hope the new one is as durable.
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