they can be rebuilt, and work fine. But replacing the alt on the XK is not like most cars. Theres very little room and tou have to work from below. Another thing to consider is that I drive hard in the canyons of SoCal and this may have led to the destruction of the 2 remanned units. The Denso has not given me any issues. After install It would start with a squeak, and then a death rattle. The denso started to make some squeaks in the morning but the new belt fixed that. No death rattle, accompanied with an alternator failure code. Thanks!