The USAF have done a study of the T67 at edwards AFB and the test pilots could find nothing wrong ,if my memory is correct they went to 20 turn spins with no recovery problems.
The biggest problem that the T67 had in the states was the fact that the americans dont like it if they did not make it !.
I am told that the reason for the T67 being withdrawd from service is that slingsbys product support was not up to the mark and the USAF had large numbers of T67 ,s sitting about waiting for parts.