I read somewhere that the sealant (stans, joes etx) should be refreshed every 3 months.
Does that mean just top it up? Or get all the old stuff out and start fresh?

I assume topping up would just keep adding extra weight?

Shake the wheel every ride. If you don’t hear sloshing, add sealant.

About a year since I last topped up and was sounding like it was getting dry, and given I was going to the Alps I added some more. Eventually I guess you’ll need to empty the dried up stuff out. Chances are you might be replacing the tyre by that point anyway.

I topped mine up just over 4 weeks ago and had a flat yesterday because there was no fluid.
I’m going to be checking every ride now on