called the supplier about the issue, the service tech mentioned that it could not be caused by the bearings or bores being out of line and to email photos of the wear.
decided to take the plunge "as it would be a pain if the lathe had to be returned for repairs", and lapped the spindle taper using fine metal polish and oil,
Switched from the adapter and mt5 test bar frequently for about 1/2 hr, and ran the lathe on 100 rpm.
It worked, the adapter stays tight even at the highest rev, and takes a dam hard hit to remove.
what ever it was, it must have been out by a fraction, as the fine metal polish does not remove much material.