As Imalama said, I'd bet that the problem is related to the swashplate. If you're drifting left then the swashplate is likely tilted a bit in that direction. There are two linkages connecting to your swashplate. The port (left) side one controls forward and backward movement. The starboard (right) side one controls left and right movement. To correct for a leftward drift, you would want to shorten the starboard side linkage a little bit (by turning it CW, if memory serves). You'll have to experiment a bit to find the sweet spot, but it shouldn't bee too much trouble.

If the problem also includes forward drift, as the original poster mentioned, then that can be corrected by shortening the port side linkage in the same way.

I had the same problem on my Hunter after I installed the turbo shaft, which is pretty much the same as the co-comanche and the lama, except for the body style.

-jd