I think I see something that looks like what you're talking about at 13:55 in this video:
2019 Union Pacific Big Boy 4014 The Great Race to Ogden Fifth Day Compilation: [
www.youtube.com], but it's on the fireman's side. At 16:16, you can see the similar one on the engineer's side.
Here's the Google search for [4014 lubricator]: [
www.google.com]
In this pre-departure from OERM vid, Ed Dickens describes the four lubricators on 4014: [
www.youtube.com].
Check out the still photo of the left-side area in question on this page: [
4dpnr.com].