1 ... the slimline's transmission was not pressed in far enough to extend out of the tip of the nib. Take the back of the pen off, REMOVE THE REFILL (it can't take the pressure of pressing), and press the transmission in further. Take it in very small increments, as you don't want to press it in too far.
2 ... You forgot to ream the brass tube to remove any and all glue obstructing the opening before pressing the finial and clip assembly. You should go ahead and disassemble the back of the pen, clean the dried/cured glue out of the barrel, and then you could press your parts again. The crack will possibly disappear when you disassemble it, as it may no longer be under pressure from inside ... you can reinforce the wood with some CA (superglue) to try to ensure that the crack will not spread again and be visible. I suggest that you may be able to "hide" any visible crack or seam by orienting the clip to cover that section of the pen barrel.
Cleaning/reaming each end of each barrel before any assembly or even mounting on the lathe can help with so many issues ... turning out of round, binding on the mechanism, too much pressure when pressing parts, causing finish or barrel itself to crack or fail, ect. It's an important part to remember!
Also, if you closely examine the transmission of the pen kit (and the instructions for assembly), it will give you estimated numbers for how far to push the transmission in ... but the best way is to just press it in a little, and check with the refill to see how far you still have to go. Turn it all the way to extend it as far as it can go, when checking. Always remove it before you try to press it in again. You'll learn from experience soon that you can typically press it in to a certain point (I generally press it till the brass part is inside the tube completely) and then start checking to see how much more you need to go.
Both issues are merely a matter of experience, which you are gaining quickly ... good luck, and welcome to your new addiction. For additional assistance in how to get in over your head, please click the link in my signature!
(edit - bushings) I also noticed, in examining the pics closely, that your barrels are a bit proud of the bushings ... typically you want to at least get close to the bushings, with your lathe chisels, and then take it down the rest of the way with sandpaper. Try not to actually hit the bushings or sand them directly too much, as that can change their size and then you'ld need to replace them. Good Luck!
