You don't want to spray anything in there. I doubt it's a sticking problem unless the disc is grease soaked, even then they don't usually stick (a stuck clutch is caused from sitting and rusting, once it breaks loose it will work normally).
Like Jerry said, check the freeplay adjustment, should be about 3/4 in between the pedal and the stop. A little less won't hurt as long as it's not riding the throwout bearing.
Have you had the engine out? If so, the disc may have gotten bent or the pilot bearing damaged during reassembly.
The mechanical clunk doesn't sound good. Could be a problem with the pressure plate.
Either way, you can run it and see if it gets better, or worse... Or take it apart and see what's happening.