Philip;
Is the rod seat turning only, not the cork?
I'm only a novice at rod building so may be off base. If only the seat is turning it may have come loose from the butt section and about to come right off! If this were to happen the fix would be easy. It may be that not enough epoxy was used during the build.
Check out Al Campbel's rod building over in Features. The section on assembling the grip may be helpful in understanding how it goes togather and what is on the inside.