click on my earlier link it states that it can be left in the system and the manufacturer recommends adding their own brands for corrosion prevention
If you don't drain it out, and flush, then all the sludge is still in the system and will eventually settle again as the X400 loses its power over time, so you were wasting your time putting it in.
AFAICT the manufacturers mean that it will not actually cause any additional damage if you leave it in, though.
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