does the tube have an anti-glare cover in front of it?
the tube it'self is a sealed unit .... condensation is either impossible ..... or if it's a reconed tube that has got moisture in it as part of the process.... with 40,000v+ in there and a heater coil - it's a potential bomb
(an exploding tube isn't something you want to be sat in front of!!)
it could be a "brown" spot where the phosphor is burned ...
but I think it needs to go back
If you can imagine condensation on a window, that is exactly what it looks like.
There isn't an anti glare cover on the front. I think going by your answer, I had better return it. I do not want a glass screen blowing up in my face or my daughters.