Now that I know the answer to my own question, I'll post it for the benefit of anyone else who encounters this.
I recently installed a new clutch system and McLeod hydraulic throw out bearing (bolt on). Within 200 miles, a significant amount of transmission fluid leaked from the front of the transmission into the bell housing / scattershield. On removing the throw out bearing (TOB), it became apparent that the leaking seal was in the TOB rather than the transmission. I spoke with McLeod tech support and learned that the seal was not correctly installed in the TOB.
The
oil seal is a rubber ring attached to a metal ring shaped like a donut. The seal is installed in the TOB by pressing the assembly into the opening in the end of the TOB nearest the transmission. When the TOB is bolted onto the front of the transmission, the rubber seal fits snugly around the shaft coming from the front of the transmission. The shaft is sized to mate with the
oil seal for the first 3/4 inch or so protruding from the transmission. The shaft diameter then diminishes as it transitions to the splines that mate with the clutch disk. If the seal assembly is pressed too deeply into the TOB, it will mate with the shaft where the diameter is too small and
oil will leak past the seal. The solution is to carefully drive the seal assembly back toward the transmission side of the TOB by gently tapping it from the back side. You can determine the correct seal position by comparing the distance of the seal from the back of the TOB to the position of the oil seal surface on the transmission shaft.