Hi, I know there is a similar thread here but slightly different problem.

I got a Cannondale Trail SL2 a few months ago and it seems like the headset always develops play in it after a ride or two. It has a RockShox Recon Silver TK fork and Tange Custom 1.5" headset.

I took the top cap off, loosened the stem and took it off too to make sure it can be pushed down to preload the bearings. There is a 3 to 5 mm gap between the top of the steerer and the top of the stem, and the top cap can be screwed down enough that the headset binds up, so I'm pretty sure the top cap is not bottoming out on the steerer. I tightened the stem bolts on pretty tight to the steerer by hand but not sure of the actual torque. It must be pretty high since it almost looks like the ends of the stem are coming in towards each other instead of perfectly parallel (too tight?).

When I get it to turn freely, it seems like there might almost be an imperceptible amount of play when I rock the bike with the front brake and feel right around the edge of the head tube and the dust cap. Then if I ride it more, it seems to always develop visible play with the rock-it-with-brakes-applied test.

TL;DR: Why does the headset seem tight upon assembly/adjustment but seemingly always develops play? Is my stem slipping up the steerer? I've just tried some carbon assembly paste to see if that makes any difference. Is something in the wrong order/missing? Fork crown race not seated properly? Do I have an ovalized head tube (wouldn't it always have play from the start with an ovalized HT)? I guess I should just take it back to the shop, but that is a pain... ughhh... Thanks for your help!