Fine tuning azimuth

I am finding that I have to fine-tune azimuth quite frequently for stability of recordings in the right and left channels. Even the slightest amount off, and the balance is lost, with individual instruments losing a precision and full volume that they should have. Is it normal for this to be so sensitive and to need re-adjustment fairly often? Also, does the orientation of the grove vary significantly from record to record, resulting in azimuth differing between records? I'm using a VPI TNT/Wheaton Triplanar/Transfiguration Phoenix (the latter with maybe 40 hours use).