what are the brown spots like this telling me? ......

Well, it's telling you that it needs more calcium but since, in your diary, you say you're going to start flushing, I wouldn't bother to do anything about it. For future reference, if you get this type of deficiency, it's going to be caused by either too much nitrogen causing a lockout in which case you'd need to flush and then reduce the amount of nitrogen you're providing ... or it's caused by a pH level that is either lower than 6.0 (6.2 would be perfect) or higher than 7.0 as calcium cannot be absorbed by weed when the pH is out of that range... When you get a calcium deficiency, resist the urge to just throw some calmag at it... figure out WHY it exists and take the necessary steps to correct the cause... but if you find that everything is ok - not too much nitrogen, pH is perfect - THEN you can add some calmag to your nutrients.. Good luck with the harvest... sounds like you're almost there!