You did check the fluid?
I believe the brake and clutch share a common reservoir, like on my 124.
The prior owner (my aunt) had the same problem, and I wound up being tasked with fixing it. Scratched my head for a while looking for the clutch reservoir, then realized the situation.
Clutch feeds from higher than the brakes, so it fails first, as it should! Level does not need to be super low to cutoff clutch fluid supply.

If not the fluid, it will almost certainly be the slave. Clutch masters rarely fail, in my experience. Internally, slaves are subjected to the moisture and crud than settles to the lowest point in the system. Externally, slaves take more of a beating from splashing and road grime.

Best of luck.

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1986 300E 5-Speed 240k mi.