Once you purchase something from Steam, you can not purchase it again, even if you delete it.
Even if you delete it, the next time Steam does any kind of update, or you do a verify game cache, it will download that DLC again.
There is a problem with the Dash9 right now. You're not the only one having this issue, as discussed in this thread
viewtopic.php?f=6&t=6061 which I've already posted a link to in another one of your posts about this same problem.
If you read over that thread you will see you're not the only one.