I have a 2000 Accord with about 65000 miles on it, 5 speed manual. The clutch is getting flaky. One time recently, it went to the floor and stayed there until I pulled the pedal back out. Then it worked fine for many days. Dealer could not get the problem to repeat; no leaks found. But now sometimes it is hard to get the car in gear (especially reverse), or the clutch feels spongy, but not in a consistent way.
Something is deteriorating in either the clutch master cylinder or its slave cylinder. Even though the dealer did not find the leak, there is one. It may be internal in the master cylinder.
When one goes, the other is probably not far behind. You might want to just replace both.
However, you could try and flush and bleed the clutch system. It is easy to do and if it works, you save a lot of money.
My daughters 98 accord just went through this ( sticking to the floor ) clutch master cylinder is plastic. Honda did a redisign in metal. The only place to get it is the dealer, and it comes with new metal clutch master cylinder, metal slave cylinder, and line between the two. Good news all is fixed. Bad news dealer only part ( kit ) $398.00