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Gso 12
I have a Bintel 12" and it works fine optically, albeit I use it in darker sky than you describe. So there is still no convincing explanation for your apparent inferior views, altho the mismatch of expectation and reality remains possible, as mentioned.
Other options:
Your optics (primary and/or secondary) could be severely pinched by the mirror cell and/or secondary holder, respectively. In the past this was a pervasive problem with the economy optics from China, but I believe it was largely remedied. Still, worth a check, if you feel comfy removing things. The primary mirror clips - with a rubber pad cushion - should be loose enough to slide a piece of paper between the under surface of the rubber pad and the mirror. The secondary clips should be similarly loose, but tight enough to prevent any movement of the mirror as the scope moves up and down. And give the secondary holder and spider (separately) a little wiggle, to see if there is any loose element like an overly-floppy secondary bolt spring or stripped thread on a collimation bolt.
Your mirror could be a lemon - a terribly poorly figured mirror, which slipped thru GSO's quality assurance system. Daytime assessment of collimation would not detect this. Really, only a star test would, and you would need a clear night to pursue this.
The collimation issue sounds like it's less likely the culprit now...however, the GSO does have floppy primary springs, as discussed, and the secondary spring also is no winner, leading to potentially clunky collimation. But one assumes the Bintel check of collimation would pick that up. And that is easily confirmed by an in-field collimation check. I suspect that collimation isn't your main issue, from what you've described and shared re your focuser tube views as you have provided.
Can you make a trip - without your 12 - to a club site to look thru others' 12 and comparable scopes, to assess the expectations/reality issue?
S
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