Aha! Fixed it!
Here’s the instructions to save anyone else the hassle.
To fix the arm, I had to take off the bottom seat support, then remove all the other screws and use a screwdriver to hold the screw and turn the arm to maximize leverage. When I got it out, I saw it was slightly bent, and I suppose had been half put in to a point where the threads were catching. With the arm off, I screwed it back in, making new threads by applying a bit of force. Then I could put it all back together (putting the seat support on is a pain though as all 4 screws must go in perfect or they get caught on the soft aluminum threads).
Fixing the wobbly was easy, with the right tool. I first got a pair of adjustable (replacement head) spring clip pliers, but they were too bulk to fit into the recessed seat post. Then I tried small nails, but impossible to get leverage. Then I tried (4 times) crazy gluing pins onto the end of a needle nose pliers. I tried fishing around with forks, knives, jeweler screwdrivers…
…finally found a proper tool shop and got a very pointy needle nosed pliers.
It was working, but the width of the handle made it impossible to spread the pliers to remove the external spring clip. I trimmed the handle plastic with an exacto.
Once off, I could see the seatpost assembly. I dunno what HM was talking about, there is no permanent press-fit plastic part. Instead. There are 2 plastic collets. Both seemed in good condition (the slit is not a crack, it is the exact same on both chairs and both parts).
I have honestly no idea what the problem is, as everything looked intact, only thing I can thing of if there was somehow some part missing, but have no idea how it would get out. The spring clips and inside did not look tampered with. Just seemed like a tolerance issue.
To fix, I just wrapped a few layers of plumbing teflon tape around, and… done. Now the fit is tight, still swivels, no wobble and the teflon tape should hold up well to the bit of friction I think. I didn’t replace the spring clips (apparently also called Jesus Clips, becuase when you try to get them off they go flying and make you say “Jesus!!!”), incase the teflon tape wears over time and I need to add more tape.
Total cost of fix.
$12.99 for pliers
$0.69 teflon tape
$13.68
I have no idea what HM would have said if they came, other than to try to get me to buy a whole new base or something. I am going to speak to them on Monday and see if I can get an exploded view of the assembly to at least figure out what possibly could have gone wrong. I know they can supply exploded part views to order replacement parts.
If anyone has an idea why there was an issue in the first place, I’d be very interested to hear. Even though it’s fixed, I’m curious.
R
Pics below-
