Probable PayPal Claim

My experience, advice:

Forget everything that has gone before, i.e. start fresh.

Make the claim asap, 

Imagine PayPal agent opening up and reading what it is about. Reduce your claim to the fewest words you can.

state what you want 1st. Full Refund

state justification for your request. prove the problem, again, simply.

now, like an addendum, some backup

presumably you have copies in writing, assurances  from seller to attach to your claim, in the original ad, and any questions/answers in writing, via eBay messages: both before purchase and after problem discovered.

don't even mention how/why/what the money moves, that will happen via PayPal's methods when they make a decision.

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Now, I hope you fund your PayPal with your best credit card (not bank ...) Notify your credit card company a PayPal claim has been made. They approach it as FRAUD, and start a countdown, say 14 days. After that they contact PayPal. PayPal threatens seller to resolve the issue or PayPal will close their account.

Meanwhile, CC company puts a hold on the transaction. You will not have to pay the charge until the matter is resolved.

Best of luck with this.

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Everything I buy, I PURPOSELY ask questions in writing via eBay messages to have those questions/answers in the system in case an issue appears.

You sending it back to the Manufacturer (rather than the seller):

Essentially that would be a warranty claim, and most companies warranty's are NOT transferrable. If not transferrable, best to return to seller, get a full refund and go shopping. Let seller handle a warranty claim for himself, then sell it to someone else.

Sooooo

1. even fixed, do you want that model?

2. IF you want it if fixed: you could discuss with the Manufacturer a transfer of the warranty to you. (now for this fix and for the warranty's duration remaining). If the maker is responsive, I would probably go for that.