Nad C160 preamp switching problems

I presume that it's a C160 you have?
I actually sold this unit through ebay and the buyer's insisting that it's not 100% o.k. and he would like his money back or reimbursement for repair of the unit. I suggested he use another input rather than the tuner or turn the tuner off when not in use, but he refuses. NAD's been no help, telling me that the warranty's up and the unit is now out of Canada and in the U.S. so any warranty is not transferrable. They also refuse to acknowledge that there's any chronic problem with the unit, even though it is mentioned on some consumer reviews that they did realize intially in production that there were problems with capacitors, which caused the switching problems, and that they did change capacitors to rectify the problem.
I never had a tuner plugged into the preamp before I sold it, so guess I'm kind of screwed on all this.

I have a similar problem when I switch to one of the tape loops. I find that if I change to the desired input and turn the pre off and back on after a few seconds, the switch is made. It's kind of a pain, but since I don't realy use tapes anymore it's not really a big deal for me. The other selections work fine.