Hi Ron,
I would like to contribute .
I would suggest two related to the effectivess and efficiency.
One could be the rate of RMA on the product sold to the customer, another could be related to the responde time in case of an issue that caused a material return, for istance to respond to non conformity generated according to the problem solving method/process agreed with the customer in a certain time base ( 1 working week for corrective action plan , 24 hrs for containment etc...).
Hope this helps