losing clutch at low idle

[Brian1973]

1991 3.0 5 speed. I've never experienced this before... Every once in a while, seems I'm loosing my clutch.... pedal doesn't engage until the very last few inches of pedal... To the point that I can almost not shift.... Seems to only happen currently sporadically and idle is usually low. If I press on gas a bit and gun it a few times, I seem to get it back... Master Cylinder? Maybe bad fluid, looks a bit yucky... Changed clutch a few years ago, that should be fine.... the sporadic nature is throwing me a bit but I'm leaning towards the master cylinder going bad, right?