Here's a blast from the past - a very clean Criterion CP4 barlow. The paint is unmarked and the lenses clean except for just a bit of dust. About the only things I can see that prevent it from being in "like new" condition are a slight discoloration on the inside of the tube (not near the lens) and some extremely tiny bubbles on the edge where the lens meets the aluminium housing. I have to believe it is one of the cleanest examples you'll find for something that is probably 20-25 years old. I can also include the lens cap it has been stored with.
$30 shipped in US; check, MO, or Paypal accepted.