Gentlemen (you know who you are & DO NOT PM ME REGARDING MD2020 OR RELATED THREADS) - I hate to be heavy-handed, but if another MD2020 thread has to be locked due to personal attacks, at least 3 of you will be affected as well. Please stop the personal attacks now. Final warning.
I noticed a couple of things I missed earlier -
You posted pics of 2 different inserts & used the later version (I think the earlier would have been more appropriate)
Based on the extremely advanced position of the regulator, it looks like there is a problem with the balance & the gib (the tiny X-shaped clip on the rotor) is not locked into place
For a watch that is regularly exposed to water (including rain or getting it wet while washing your hands), once/year is the minimum. Keep in mind that over-tightening the caseback/crown will accelerate gasket wear & a gasket that sealed yesterday may not tomorrow. In my case, for rare or important watches (that covers most of my collection), I avoid moisture altogether even though I run everything through the tester regularly.
Sounds like the threads are stripped. Could be either the crown or tube, though the tube threads are easier to see. I am not sure about 8mm crowns, but in the case of other Twin/Trip locks, you could also have a mismatch between crown & tube, where the threading for the tube begins beyond the end of the tube, which is required for some crowns.
I think the min spec is 1.5 turns for Twin/Trip locks. In addition to a crown/tube mis-match or insufficient inner tube diameter (requiring broaching), stem length (if too long) can also limit the number of crown turns.
Either the spirals of the hairspring on the balance are touching each other or adjoining components, or you may have misaligned the location of the hairspring between curb pins. If you find issues with the former, you may be able to correct them. However, if there is a problem with the curb pins, I would take the watch to a watchmaker.
Congratulations on the upcoming projects. What I can see looks very tasty.
As far as the ill-fitting 800/8000 combo goes, how well do you know the sources you purchased them from? I have never found a gen crown that did not fit its correct companion tube, which would make me question the authenticity of 1 or both parts. Sadly, while I could be wrong in your case, I have been seeing an increasing number of aftermarket parts in gen-looking packaging & I usually tell people that fitment problems are often the only indicator of this type of scam. Even long-term Rolex dealers have been fooled by some of this stuff.
Bezel diameter
Case length (lug tip to lug tip)
Case diameter (without crown)
Case thickness, measured from flat portion of crystal to caseback
Due to the insert's fragility, I cannot remove the bezel to get the bezel thickness, but I think I posted that in 1 of my Phase II constructions threads that you can search out.