I bought my tent in May 2020.  I just checked the fly & there is no flaking/hydrolysis on the seams.  How old is your tent?  I'm surprised you're experiencing this issue if your tent is only a couple of years old.   I, too, am surprised & disappointed REI is unwilling to provide anything in the way of replacement parts for our tents.  Sadly, REI only seems to direct us to 3rd parties, for the repair or replacement of anything as it pertains to our tents.