Yesterday was my first day on the field testing the Trex 600N. I was so excited to run-in the engine and hover the heli, which is actually the first RC heli I assemble. Surprisingly, the 2 bolts holding the flybar went loose and the heli started shaking. luckily I was running-in the engine and was still on the ground - no damage. Then the tail rotor hub went loose as well while the heli was on the ground also.
Lessons that I learnt:
1) I should have used a better threadlock quality while assembling the kit.
2) some parts which are pre-assembled has to be dismantled and reassembled again using threadlock or CA glue.
Consequences: I have to remove the bolts and apply a proper quality threadlock, which is certainly time consuming but part of the learning curve.
Regards.

I think most people are using the Pacer Z-42 "medium" strength thread-lock, and it is available in most local hobby shops.  It is a red bottle, but the liquid inside is blue colored.

To clean the screws, I have found that the "isopropyl alcohol" with brand name "Green Cross" works very well.  It is available in almost all pharmacies and bigger super-markets.

Just want to share. Normally if contain oil better used contact cleaner to clean the surface before apply thread lock.