Am I justified in my frustration?
If I understand this correctly, and you had 5 hours between saying "I'll take it!" And going home...you are the only one to be frustrated
The seller sold you a rebuildable core (whether or not you have the skillset to rebuild this particular core is irrelevant)
At a price you agreed to, and the seller was an individual, not a store that offers warranties
Then somehow you contacted the seller and managed to get a refund you were not entitled to, in a way some might consider harrasing
After you got the refund, with the implications that this case was now closed, you went on here to get your pound of flesh
Now, this is the way these 4 pages read to me, so if I misread anything please correct me, but as it looks to me, right now you would be the person to avoid