while tri flo is good.....
It is rather expensive .... I have used kerosene, diesel (heating oil) and one of the favorites is hydraulic fluid (oil... Or automatic transmission oil) another one with a slightly more pleasant smell is "marvel mystery oil" (basicly thin hydraulic oil with a scent added) all of these are good penetrants and are sold in at least quart quantities for the price of or less than a two ounce bottle of tri flo. I realize that you may only need a squirt..... But myself I have at time resorted to sinking an entire sewing head in a bucket. Then again I take on some things that should honestly reside in a landfill. Good luck!
Dan