Yep, dirt and such. Best is to get it cleaned, meaning opening up the side to clean and re-lube the levers and such that make the spacing happen.
In the meantime, you could take a scrap roll of film, or backing paper only, and keep running it through the camera while you watch a TV show or such. See if some repeated action will redistrubute old grease, etc. There are other tricks to attempt involving dripping Naphtha into a few palces, but it's the sort of thing that is probably of the, 'if you don't know I shouldn't tell you' type. And it is hack and prone to cause more problems than it solves.
Going inside a Rolleicord is not difficult if that kind of activity comes easily to you.