I have a couple of Eotechs and I have seen some spotting on the glass.
It is USUALLY some spatter from what ever you used to lube a gun.
It is sometimes surprisingly difficult to get it off the glass.
What I have found that works pretty good is the wet lens wipes you can find for eyeglasses. You can find them at any drug store.
Sometimes though, they just move the spot around.
I have used Windex, sprayed on a lint free cloth and light wiping.
I am betting you have some contamination on the outside of the glass and you may have to work a little to get it clean.