The "flat sided" V and S series have the 4 speed auto. Any Dex/Merc will work just fine. I always used the house brand Dex/Merc from AutoZone or wherever. It's the cheapest option for the 4 speed.
If it's the "muscular shouldered", curvy sided Volvos with the 5 speed the Toyota T-IV or Valvoline MaxLife LV (red jug) or "original" Mobil 3309 (the specced fluid) is what you need.
Yes, the MaxLife LV (red jug) will work in either so just use that if it's available. People on the Volvo boards get all bent out of shape over this and it's not necessary.
There is no serviceable filter in these units.
In the case of the 4 speed the upper cooling line is the one coming OUT FROM the transmission. You can depress the green catch on the line and pull it out of the radiator.
Have a 3 foot length of 5/8" tubing ready, set one end in boiling water to soften it and stretch it over the end of the cooling line.
Now you can do a pump out 2 quarts at a time. It's easy to do.
If you're enterprising you can do a drain and fill first and start the process with clean fluid.
It's really cool to see the black, wretched fluid turn red in the tubing.
Have ready the 2 "O" rings which are at the end of the cooling line.
Remove the old, hard ones with a plastic or wooden pick.
Kira