NAD T765 AVR replacement fan?

I have a bad fan on my T765 that whirrs loudly upon startup until after a couple minutes, it slows to a halt.
I don't know how to determine what replacement fan to get (manual does not mention, Google failed me).
I also have a T775 that may have a fan that's going as it started to get noisy the other day.
Any advice on which fan to get, and where would be very much appreciated.
TIA!