I recently re-authorized (in iTunes) my 4,1 --> flashed 5,1 High Sierra CMP and noticed an alarming phenomenon. All had been well with the machine and things looked fine after the authorization but I soon noticed that free space on my boot SSD (a 500GB Mercury Extreme Pro from OWC) had shrunk very significantly during the course of a few hours afterwards. Free space had been around 50-60% but it went down to 25%. I do not have a lot of stuff from the music store in iTunes and when I actually tallied things up, it was not more than a few gigs worth of music. Ditto for other types of content. Files I create are mostly always stored on internal HDs when done, so this is a mystery. I also cleaned up my email newsletter subscription and deleted a fair amount of useless stuff but no dent on free space. To make matters worse, the free space continued to shrink over the next couple hours until I got a message from TechTool Pro that my disk usage limit of 85% I set had been exceeded and I now had 14% free space left. Now I'm down to 7%. Would be very grateful if someone could clue me in as to what the heck is happening. I picked up a 1TB drive on sale yesterday and am planning on cloning my boot drive to it and replacing. Wondering if there's anything I need to fix before doing so.