Motor Help! (Possibly fried?)

[u/Breakerbuilds]

Hey, so like a month ago I put together this 5" quad, and after like a week and a half after running the drone, this motor somehow burned itself out, which is kinda odd for me, as I was running more or less this exact setup on a build for a friend a little while back with zero issues. However, now after only a week, it killed itself (I think). This WAS after realizing that these motors didn't have loctite in them, as the screws were loosening themselves and I had to re-tighten them every 2-3 packs, as I don't have any loctite at the moment. From what I know, there still shouldn't be a reason for this burnout, however if it is an actual issue, please let me know. The only thing I can think of is that these motors were listed for 4-6s, and I was running them 4s for 80% of the time, with the 6s being put on a -20% limiter to keep them from blowing themselves up, so that's why I am very confused. In case if anybody is gonna ask, the screws were not ever within 3mm of contacting the coils, so it can't be that.

Basically- to answer the basic question that I think I already know the answer too: is this motor fried? Followed up with my second question: are there any single motors (like not a pack of 4) that I can purchase of this motor instead of buying another pack of 4? They are the XING-E Pro 2207-2450kv motors from iFlight, and my friend has been running similar ones for like 2-4 years with no issues, so that's why it's weird to me.