I've found parts to be quite tricky - luckily not much has gone wrong with mine so far, but if any used major components come up on ebay for cheap i tend to add it to the parts store if I can. Classicswede has a lot of bushes and suspension components for the 960. Euro car parts has your generic brake pads and discs etc but nothing critical or bespoke. There may be other resources available that I'm not aware of.
Rust is worse than the 940, not sure why this is... it'll weld... maybe!
Fuel economy is absolutely horrendous, and performance isn't that great either in all honesty, and I have the 3.0.
I have a 1992 940, 1995 960 and a 1997 V70 T5, and the 960 is objectively the worst out of all of them, however I still love it and would have it over anything else on the road... apart from the 940 or the V70 T5.
I paid £400 for mine two years ago and it owes me nothing, but I wouldn't pay what some of them are being advertised for on ebay, mostly due to the parts issue.
I sincerely hope someone else comes along and tells me I'm talking garbage, and there are plenty of parts available, in which case yay I can keep it for longer!