I bought the Luxman 505z from Japan off Ebay 6 months ago from a highly rated seller, similar to your situation. I obsessed a bit about warranty support and transformers. In the end I bought it with zero regrets, zero problems, and great clean effortless power and sound. I do not care about lack of US warranty support because the odds of a working unit breaking down under warranty is less than the chance of a lightening bolt knocking it out. Luxman's are well built, solid amps. I figured buying a US model was like paying for a $3,000 warranty and I would not put money on that bet paying off. Those good Ebay sellers offer 30 to 60 day returns often including shipping. You have Ebay fraud protection. You have credit card protection. Transformer is a non issue. Do you want to pluck down a few thousand to cover a Luxman amp breaking down? They don't break down easily.
Anyway, for me, I would do it again. In fact, I am looking at a Luxman turntable since I already have the transformer for the 505z.
Do check the duty situation into the US. I think it may be 15% now, but you know that could change at our leader's whim. Some sellers claim to cover this, but while they may intend to, duty is paid by you, the buyer.
For some people, buying the US version at a premium is worth totally eliminating these worries. That is a valid way to approach it for some. It just didn't work for me.

