I had a problem with my Greystone while it was still under warranty - I believe it has a two year warranty. I was able to get a new control board from the support company at
https://www.wayinterglobal.com/pages/contact-us. The support phone number is (574) 970-7108.
The control board didn't fix the issue so they sent me another control board and the switch board. That fixed it. Until I went to use it the following spring. I'd spent quite a bit of time on it and gave up. As you've noticed the Greystone is built quite cheaply.
However, I went to get my 12V converter replaced under my extended warranty the following year and discovered that the fireplace was covered, too. The shop replaced it with an equivalent Furion model and we've used it extensively while wintering here in Colorado this year.