Unless it has all new o-rings I wouldn't try pressure testing.
I bought my Nikonos new in '87 (?) and it is on the original rings - it would need a complete strip-down and re-build with new rings before it saw water again.
There are websites that show how to change the rings and grease what needs greasing.
My understanding is that new O-rings are available for the Nikonos-V. -Someone please correct me if I am wrong.
This is a beautiful camera and smaller than it looks in pictures.