Thanks for that link Wavy.
One big fat lesson I've learned is don't fool yourself by bringing in a soaking wet Dob into the house, tipping the tube aimed down to the ground to drain and air dry (aside from wipedown of outside tube) for half to one hour before covering it all up and putting it away does the trick.
I've now got mildew spots on my mirror and can only hope they will come off without having caused any damaged to my mirror.