Hydraulic clutch is out again, help

[MaSnaka]

Well the clutch has been working fine but my hydraulics has been nothing but a problem, well about every 2000 miles or so anyway. I have the Howe Racing master cylinder with a hydraulic throwout bearing. I have had to replace/rebuild this thing and bleed it 1,2,3, this will be the 4th time in the last few years. Last rebuild was 6 months ago, maybe 1500 miles. The fluid (non silicone)was flushed/changed, new O-ring plunger and return spring. Sleeved the lines with a heat shield. The cause seems to be deris getting between the o-ring and the cylinder breaking or wearing out the seal. I had to move the resevoir around because of some engine work back in Dec. and must have disturbed some crud. A month ago I had to move it around again and now this problem returns. Fortunately I ordered two sets back in Dec. so I have the parts now. Does anyone have similar problems with this Howe Racing assembly? I have a very competent shop doing the work (they came highly recommended by more than one enthusiast) and I am just perplexed everytime this thing goes out. Seems very touchy and delicate. Shouldn't it be somewhat bullet proof?

John