Digital BW, The Print

I'm making a printer work very, very hard for me right now with near 
continuous printing couple of hours at a time.  (This is when the CIS 
feels really good).  Have several days to go on this project and 
would rather NOT burn out the printer in the process. 

It's developed a 'trill' as the print head moves from right to left, 
but not the other way.  I suspect the silver guide bar could use some 
lube but don't know what kind?  Have some sewing machine oil that I 
could apply minimially but hesitating for some comment here.

Suggestions welcome & thanks in advance.

Cleavis