Nice review.
Having been using the 105 Patrior for over a year now, and it's predecessor, the 360, for five years before getting the Patriot (practically using the same brush for more than half a decade), I feel I have to comment on the portion of the review looking at the 105.
True, the trigger is held in place by just the back level and the rear spring when the needle is removed, but it seems to be quite the norm with double action brushes. In my opinion, it's not hard to put back together, the trigger being one-piece and the air valve rather easily accesible. Draw the back lever back - push it to the side to lock it in the horizontal slot - drop in the trigger - release back lever.
With the needle holder, do you mean the tube shank that screws to the airbrush body or the locking nut that secures the needle to the needle tube? What part you can't get screwed back in?
Both the trouble you reported having with that and the paint ending up in the trigger and valve space would suggest to that there's something not quite right with your sample.
On the paint leakage to the rear, is the needle bearing okay and correctly placed? That bearing should seal the paint cavity off from the rear of the brush.
I completely understand the quick review nature of the spray testing, but the pattern you got seems quite coarse and large for the 105 to me. Did you try any other paint(s) and different pressure settings?
For comparison, here's some quick doodling I did some time ago with my 105. The paint is Xtracrylix black, thinned 50/50 with tap water, and sprayed at around 15-20 psi (can't remember exactly anymore).
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Regarding your mention of the unprotected nozzle of the 105, I agree it's a bit of a drawback, but you can use the crown regulator (#41-043) of the Badger 200NH, as the brushes use the same head parts. I sent Badger email asking about more protective caps and they told me about 200NH part. I wish they'd mention this in the 105/155/360 instructions too.
However, please note that 41-043 is a
medium regulator requiring the corresponding medium needle and tip to work properly.
Talking of the needle, I found the fine needle and nozzle the 105 ships with to be harder to spray with my usual model paints of choice. Of course, it could be just a matter of thinning down my paints more and playing around with my operating pressure settings, but I just went bought the medium needle, nozzle and regulator to get back to the spraying properties I grow accustomed to with my earlier 360. I've found that to perform well from Luftwaffe mottling to more single color overall coats.