I've read and re-read your post, and I am struggling to figure out exactly what it is you are talking about. Those pictures will certainly help.
For a crack to continue propagating there must be a force that keeps pushing through.
Are you talking about the corrector plate? I just cannot think about anywhere else a crack could appear.
If this is the case, then the solution is a very easy one - remove the corrector plate retention ring!
If the corrector is cracking this is because the screws that hold the retention ring screws are wound in WAY TOO TIGHT. These screws need to be ONLY finger tight, not wrist crushing tight. Remember, these screws are pushing on to glass.
Another thing about these screws being wound in too tight is this will be inducing a strain into the glass which will be distorting the corrector plate. So while you may think that the image the scope is producing is good, with the corrector plate being distorted you really have no idea just how much better the image CAN be!
This exact same problem occurred to a Meade SCT I bought new. I struggled and struggled to get the image to play nice. Collimation "appeared" to be good, but the image was still poor, refusing to go over 175X before the image went to crap. Out of desperation one day I decided to check the secondary mirror. To my surprise I had to really lean into the screwdriver to remove those retention ring screws! . And when I lifted the retention ring itself, BLOODY HELL! There were two clamshell chips around where two of the screws pushed on the glass!!! These chips were hidden by the retention ring. I was really cross about this especially as I struggled with this scope for two blooming years, only to find the blasted thing was defective from the blooming factory, and at this stage could not make a claim on warranty. That this was a factory fault was evident to me because the chipped glass had been removed, and the retention ring replaced. When I reset the retention ring with the correct pressure on these screws, guess what? The image finally cleared up because the corrector plate was now no longer under strain.
This problem of over tight retention ring screws can affect not only SCT's but Maks as well. There will be literally thousands of instruments out there with overtightened screws distorting corrector plates, and the scopes owners are unware of this through no fault of their own, only through ignorance about not knowing not to over tighten these screws, or like me, the factory itself is to blame. I recently also fixed a mate's brand new C8 who had sought to do the right thing by cleaning the corrector plate but over tightened these screws when he replaced the retention ring. We were looking to improve the collimation that night when I noticed something odd about the image of the defocused star. So I asked him if he had done anything to the corrector plate when he told me he had and what he had done. So we backed off these screws, the corrector was freed from the strain, and the image improve straight away without tweaking the collimation screws. Now his C8 is humming nicely.
As for keeping your scope outside, how exactly are you doing this? I would rather know first how you are looking after the scope with it being "outside" before saying anything more here. There are just too many variables.
Edited by maroubra_boy, 19 April 2021 - 06:40 AM.