leaking clutch

I have a puzzling leak of brake fluid from the hydraulic clutch release bearing on my 512TR. I upgraded to the 512M clutch/bearing assembly when I did the major rebuild 9000+ miles ago (2 years) and it's worked perfectly since. Four weeks ago I got in after a 10 day hiatus from driving the beast and found a small puddle on the floor and no clutch pedal. After pumping the pedal 5 or 6 times, it came up and worked fine for another few weeks, so I figured a piece of dirt got into the seals. Last week it happened again after only 3 days of no driving. If I use the car every day all seems well - not a drop on the floor and full pedal. Bad seal? Any other thoughts?