Quick question/update: I checked the actual radiator, Coolant is orange and no flakes, quite clear. BUT: it's only good to -20 and there's a very cold snap coming BEFORE my appointment to get it flushed. Can I top it off with the green coolant I have on hand for a week or so? (I don't think the orange coolant was for the 2nd gens, correct me if I'm wrong..). Got to do this today or tomorrow. Also, puzzled why the reservoir look so dirty but the coolant fluid IN the radiator looks fine)
The reservoir has very little flow into and out of it, sediment will build up in that over time, it's no big deal. That's almost easy to clean out, pull the drain hose off of it with one hand, with a pan underneath to catch most of what comes out. Use a water hose and spray into the reservoir, with one hand covering the opening above the hose sprayer(to keep you dry). Then it's clean, push the hose back on, and fill it as needed to the cold level mark.
The coolant you have is likely fine to mix something new with it, the odd chemical kind is not common and I doubt you have that. So depending on what the low temps will hit, you can add as needed with the green, or the yellow cheap Prestone we mentioned before.
I had my first car with about that same level of anti-freeze in 1981, when the low one night hit -24*, no harm at all. I think the low temp has to be well below the actual coolant rating, for a long time, to freeze it and crack something(the plastic tanks are the weakest links).
If you are very worried, it's not hard to drain some coolant out, and refill with pure anti-freeze to lower the rating of the coolant. The petcock at the bottom right rear corner can be loosened with any decent pair of pliers, and a drain pan.