Hi Ken,
If it's faulty and the guys at CPT can repair it for a reasonable charge then go for it. However, in your shoes I'd not let them start replacing caps, wiring or OP amps for several reasons.
Firstly and most importantly, there is no 'best' cap or op amp only the best choice for that
particular circuit. That may turn out to be an expensive high speed modern IC at £10 a throw or it might the the ubiquitous NE5534 at 50p.
In a premium product such as the NAD S series the designer will usually spec the best part for the job as opposed to the cheapest.
Same goes for caps.
Wiring is ....... being tactful.... a very personal thing

I think its mostly a load of old fooey.