Buff,
CA glue is cyanoacrylate glue, aka superglue. It's very strong obviously, but only in a linear way. If you try to break the joint sideways, CA glue bond is then very weak, and I can therefore break the tubing off the turret and hull without any major problem. However, don't go crazy with the CA glue. A drop is more than enough. In fact, too much CA glue tend to take a long time to set which can be annoying!
As to the hard lines, you may just be using too weak of a mix. I use about 2 drops of dishwadshing liquid and 3-4 drops of vinegar for a shot glass of water, to which I add a pea-sized amount of paint...
I do my drybrushing with oils as soon as my wash is dry (I have little patience!). However, I'm also very gentle and se a very soft flat brush so that I'm not going through the base enamel paints I used on the vehicle camouflage. If you use acrylics as base, no problem. But enamels and oils are more dangerous a mix! However, if you do have patience, wait to make sure your base coats are fully dried before going onto the weathering with oils.
If you are very gentle and delicate, the oils that you are drybrushing will tend to appear only onto sharp edges and raised details. On large flat areas, it is good to have a bit of 'forced' definition with a bit of lighter paint in the middle of the panel. But only try to acheive this after you have done the raised bits and you are sure there's really just about no paint left in your brush! If you start there first, you'll end up with a contrast that's too strong. When I do weathering on a 1/72 AFV kit, I normally only have to dip my soft flat brush once in the oil paint. I then proceed to remove the excess in a rag then start drybrushing onto the bottom part of the hull (to test) then move onto the wheels (cause if there's still too much paint, the wheels will look the worst after dusting anyway), then slowly move onto the main, sharper, edges of the hull and turret, moving onto the smaller raised details and finaly onto the middle of the flat panels (if needed).