well, hate to say it, but it sounds like you managed to get the threads in the insert messed up. I don't know of any way to really repair the lead in that somehow got split. If you don't get any better ideas, you might try removing the first quarter turn or so of the threading with a scalpel or exacto knife to get rid of the damaged part. You might be able to clean it up enough to get it starting cleanly again. Other than that, you might buy a cheap gold plated kit and salvage the threaded insert.
Ok, just reread your post, is this something that you have problems with on multiple kits? I've never had to use any kind of lube on the threads, or heard of anybody else needing to either. I tend to start the threads by putting the cap on, and turning it backwards till i feel the threads "drop" then turn it on till tight.