This is what happened to me: (maybe i should have given up after the 4th repair kit already)
Some dev on irc told me theres three ranks of garbage so the quality of an item goes:
1 - Perfect
2 - Outstanding
3 - Cool
4 - Better
5 - Normal
6 - Bad
7 - Very bad
8 - Garbage
9 - Garbage
10 - Garbage
Now if i used five repair kits on a garbage quality item i should have received at best a "cool" item but at the minimum a "normal" item. The Turbo Plasma stayed at garbage however. Which makes me think either some items are bugged and cannot be repaired OR the number of garbage ranks is not limited to 3 but can stack up to ridiculous values.