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If you can afford to pay 4k for a spa, you can pay another 2k-3k for the warranty too.
Btm line is it's a hot tub, doesn't matter what brand it is, and it doesn't matter how much you spent on it, things will and can fail. Ironically it's seems to always happen just after the warranty has expired. This usually makes for the more pissed off customer. Sorry your having troubles with it, and if they do cover it under warranty cudo's to them. That being said it is out of warranty, and they really don't have to, but then knowing it has been on-going it might make a difference..
Piece of cake to put that motor in. Do the dealer a solid and volunteer. Familiarize yourself with your now out of warranty tub.