Re the suggestion that the OP gets a good ED scope instead:
The closest contender is probably the SW ED100 f/9 which I also happen to own. IMO the mechanical quality and finish of my Vixen scopes is somewhat better. Yes, the ED100 has a crayford-like focuser but I find the R&P focuser on the Vixen is more enjoyable to use and less fiddly to adjust. Paint-job on the Vixen is somewhat better too. As for optical quality, the ED100 has noticeably less false color (although it still has some), but optical quality is not in entirely the same league as high-end optics: Expect some SA and less clearly defined splits of tight doubles. Also I find the contrast is not entirely on par with high-end optics. I found the same to be true with my 80ED: very modest CA, some SA and decent optics that were still noticeably outperformed by my SD81S. Now, don't get me wrong: the ED100 is very nice for what you pay, just don't expect world-class optical quality for a fraction of the cost.
IMO you are doing well to go for optical quality and you are right to expect excellent optics when paying a price-premium for Japan-made optics by Vixen. And in my own experience you are not likely to get optical quality on par with that if buying an entry-level ED scope instead. I've owned a handful of Chinese-made scopes over the years (all bought from new), and not one of them has performed at the same high level as my Vixen/Tak scopes.
If I were In your shoes I would hold off making a decision to abandon the A105M for a bit longer. It seems more sensible to first verify that there indeed is a problem with the scope's optics (and be sure to eliminate all other factors, like diagonal, thermal issues, seeing, problems with your own eye-sight, etc). You may also consider to do an in-doors artificial star test, looking for the ragged/non-circular diffraction discs reported in the OP. And if there indeed is an optical problem, make sure to give your dealer a chance to set things right.
Edited by db2005, 21 May 2020 - 08:50 AM.