I like these games of "guess my most vaguely described symptom" - it helps pass the time. lol
You haven't mentioned how the clutch was operating, nor the size of the oil leak, nor where it's coming from other than an indirect way, vaguely, and those are crucial to understanding your problem more.
At a guess you have already had the problem fixed, but here's my guess, interested to know if I hit it:
For this symptom If it was grinding and wouldn't go into gear with the clutch depressed, and the pedal is soft or feels loose, and goes to the floor easily, unlike when it was working, and if the oil leak is minor and the brake fuild level in the reservoir is reasonable, it is usually the thrust bearing worn out or its yoke is broken. If the brake fluid has drained out, then the hydraulic fluid leaked out of the clutch slave cylinder, since you suspect the driveshaft seal y9u lead us to think it is at low level, but if there is a leak from higher up then it is likely leaking from the clutch master cylinder.
Otherwise, depending on the actual type of the grinding noise, and if gear can be selected, then it was most probably your clutch plates contaminated with oil and slipping so the car goes nowhere. You would have founnd it was slipping before and getting worse. But if there was no significant oil loss and the metal on metal grinding is quite loud, then It is probebly worn out, would produce a smooth continual oscillating metal on metal grinding noise when the clutch is released in gear, if you have ever heard brake disc / pad grinding it is similar but quieter.
A drive shaft seal would not be connected to the clutch mechanism.
Which one was right? If none oif these, what was the cause and what were the true symptoms?