2012 Cascadia Spongy Clutch Issue

2012 Cascadia DD15 engine, 10 speed eaton, has 635k miles on it. The other day I just delivered my load and was getting ready to leave and the truck would not go into gear. Popped the hood, Clutch Master Cylinder was bone dry and greasy inside. Added some fluid was able to ease the truck to a shop near my house. The clutch was spongy, very soft and could be pushed down with very little resistance. He inspected the line and bled the line to make sure there was no air in the line. I drove it for 2 days it was normal.

Last night, the clutch went soft again, check the fluid it was still full but the clutch was soft and hard to get into gear. I have an appointment with a local transmission shop on Monday. I was wondering has anyone ever experienced this, or what the possible issue could be? While driving it the clutch does not slip, its just a very spongy clutch pedal and difficulty going into gear. Is the clutch shot?