One thing is to never ever tighten fully then back off, it weakens the screw with the extra strain say the HB people...they should know
. I'd replace the diff plates or sand them, replace the nut and spring. Just tighten so when you have 2 allen drivers through the diff outdrives you can't rotate the pulley. Check in the car by holding one wheel and the spur then try and rotate the other wheel. If you can rotate it tighten it
Charles