OK, I have fitted the Kemet (BHC) capacitors to the NAP 160 and there is a small improvement in sound quality. I would say it sounds smoother and more authoritative, but the difference is definitely not night and day. It was worth the outlay for peace of mind (another 15+ years of use!). Thanks all.
By the way, comparing the sound of the 160 and 250 (also recently serviced), they are definitely different, but I wouldn't say the 160 is definitely better, which seems to be the consensus here (on numerous other threads). The 250 definitely sounds richer and more bass-heavy. I think each probably suits a different kind of music/speaker combination etc. I've noticed also that the 160 sounds a bit thin at high volume levels compared to the 250 - I guess due to the regulated PS in the 250. Anyway, I'm digressing from this thread..
