On our DC2 Type track cars on which we have kept the multichannel ABS, we find that successive slow bleeds, followed by deliberate activation of the ABS between the bleeds, will remove the air locks that will cause the symptoms that the original poster described.
My personal track car is an '00 ITR on which the ABS is fully operational in the most stalwart fashion after 100,000 miles...most of them on the track.
As the cars age, mechanics and dealers are going to fall back to the component replacement phase of things in order to eliminate subsequent complaints and because, quite frankly, we have lost most of the mechanics who were enthusiastic about the DC2.
If I were the original poster, I would inspect everything for proper fitment and look for small leaks, and then I would try the successive bleeds with ABS applications in between to see if that helps.
I doubt the pump itself is going...these things obviously can stand up to 100,000 miles of abuse. :-)