Coolant / Refrigerant

[Arcticdude]

Correct, the sight glass is for the radiator. You can unscrew the fitting, remove the sight glass and clean it, just do it when your low coolant light goes off the next time. You do need to use one of the heavy duty coolants, but you need to know which type is in your system now, before you add something different. There's a bunch of different types of HD coolant, most of which are not compatible with others and will cause issues if mixed. If you can't figure out what's in there now, ideally you should drain it, flush it and put in what you want, so you know what's in there.

The refrigerant label is there because that's the only conspicuous place to put it.

As far as losing coolant, there should be essentially no coolant loss. If you're losing some, then I'd start checking all the hose clamps to see if that's where it's going, otherwise I'd be taking a very close look at the inside of the radiator to ensure it's not starting to fail. The gaskets where the radiator tanks bolt to the core is another area to closely inspect. A couple spots of seepage can cause big issues and are easy to fix.