Have an Erie 610 switcher locomotive that I bought used on ebay.    Intermittently, it just 'buzzes' and doesn't move but after fiddling with the transformer/relay-looking structure in the middle, then seems to 'loosen up' and work.    I'm obviously not an expert on this, but seems like it has something to do with the mechanical structure that controls whether the locomotive goes 1 way or 2 directions.     Any advice as what to clean or lubricate or replace would be appreciated ...

For edp458

This is a good explanation of how the e-unit works (the relay looking structure you mentioned).
https://dfarq.homeip.net/how-does-a-lionel-e-unit-work/

Sounds like you're new to this. Below is a link to an old Popular Science reference article from 1964 that gives a good basic explanation of some parts and some fixes for simple problems. This will give you a starting point if you run into additional issues.
https://archive.org/details/PopularScienceReferenceLibrary15CommonRepairsForElectricTrains1964/page/n5