[spencer]

Gary,
I had the same problem your experiencing approximately four year ago. I used up two Wilwood unit within a year. I took both units and a sample of the discolored fluid to Wilwood, they're about a 90 minute drive from me in Camarillo, CA. I ask that a tech inspect the units to determine the problem. Two tech's inspected the units and could not determine the cause for failure or the reason for the fluid turning black. As I was leaving a third tech suggested that I buy their rebuilding kit, he said the unit should be rebuilt once a year and if the car is being raced it should be inspected / rebuild more often. So I bought three rebuild kits and rebuilt both units.
Not long after that I was talking (bench racing) to a guy that builds / races salt flat cars. He suggested that I have a brass sleeve pressed in the cylinder, because this is what he found to prevent failure to cylinders. I had it done to both units at a local machine shop and I've had the same unit in since. I think it cost me $150 for both.
Oh, just for information, I'm using the Mcleod throw out bearing instead of a second cylinder for the clutch.
Another possible solution, Good Luck.....
Spence..