What does an oiler do, or mask

I purchased some 1.8mm rod to clear out clogs. I discovered that when I ran the rod down the feed path everything was not in perfect alignment. I took a torch and heated the rod and fed it up and down the feed path. I repeated this until the rod ran up and down with out hitting anything and the path was completely smooth.

First thing I noticed was the improvement in finish. I suspect this is do to reduction in drag when doing retraction. I had required an oiler before and now I no longer needed one and I was getting a better finish.