I think you got a dud my friend. My Blue convoy looks perfect with great paint apps and nice tight joints. Same thing for My KO SG Prime. I did have cracked plastic on the Black Convoy (Winterfest KO) But it was a dud most likely too. You are right about the smokestacks being extremely loose in truck mode, but my parts box doesn’t seem to mind their company. I also got the KO DIA, Shadow, and SG Purple trailers. But since my regular City Commander is not a KO, I can judge the quality differences between the two fairly. The Shoulder and Arm armor are loose. But the key is to use foam adhesive stickers on the inside of the parts to provide that extra thickness. It stays hidden and keeps em tight, problem solved. If the missile launchers are a little loose, roll a small piece of black electric tape around the peg a couple times. Easy fix.
Besides the minor issues I described, all 3 KO Trailers were top notch in my opinion.
Sorry to hear you got bad CHMS seekers. Must have been more duds. Only problems I had, was with the yellow version of Sunstorm. It suffers from the “gold plastic syndrome”. I wouldn’t advise bending the elbows on that particular version. The joint will crack. Also the ghost Starscreams are prone to cracking at the elbow because of weak clear plastic. But only the starscreams. I Had no problems with the ghost Skywarp, ghost Thundercracker, or ghost Coneheads. I guess only the clear white plastic mix was weak. I’ve had pretty good luck with CHMS and KOLD considering, the amount of figures I have purchased from them through KO Toys in the past. (around 50) Mike from KO Toys always used send me replacement parts and figures whenever I had an issue. He knew that I was a serious customer and valued my business. I can only speak for my own experiences with KO Toys.