I wonder if anyone can help me on a year by year basis with s80 options vs
features?

Can anyone tell me or refer me to a site that lists past model years and
what was std vs optional? I am limiting myself to 2000 and newer ( I recall
99 had serious transmission problems, am I correct that this was resolved
for 2000 model cars and newer?)

I am specifically curious about a few items:

AWD, I am going to guess that this was an option for any of the years it is
available on, Which years though? Is the system reliable long lived and
function well? Was it ever the viscous coupling like some years of the 70
series had that had some issues?

Side curtain airbags (not sure of the proper name), What years and any
problems with them working as one would expect them to work?

At one time i think there was a security glass option at one time, has it
been available all a long, any thoughts on this item?

STC (stability-traction control?) what does this have over just TRACS
What years?

Any recurring issues with any part of the ac system?

Is the timing belt service interval the same over the various model years
and what is the interval for each of the years if it varied? Anyone able to
pass along current prices for this service.

Are there any systems on this series of car that has had a
problematic/costly history to rectify?

I don't expect any one person to answer all the questions I pose, and I
appreciate any information passed along.

thanks very much