Yes, once your NAP140 has been serviced then the new capacitors require some running-in and a little brightness at first is not unusual.
NACA5 is a good call - especially on an older amp like the NAP140. Do note the FAQ on this here. I would definitely try to get the Naim SA8 speaker connectors though. I’m surprised if the distributor cannot get them for you. I would ask again. Otherwise they are available by mail from some UK dealers online.