Our mechs are what would be known in engineering mechanics as low-speed and low-use systems. As such, friction never warms gears and bearings and grease doesn't flow and lubricate when it's cold. Instead, we have this:
Three spurs are stacked in this CLW box, all nicely greased. The nice cold grease merely squirts out the mesh (see it neatly deposited on the side of the teeth?) of any decently matched set of gears and forms a lovely pocket around each, but doesn't stay on the meshing or bearing surfaces.
The other half of the box; the steel shafts are bone dry where they bear on the brass which, in spite of the wisdom here, is a perfectly good low-speed/low-use bearing surface that should last almost as long as bronze-to-steel as long as the finishes are nice, the contact surfaces are better than minimal, and the interface stays lubricated. That last bit ain't happening here, and it's crucial or that familiar brass-to-steel death spiral is dam near instantaneous. Bronze-to-steel bearing surfaces equally depend on oil to last. BTW, see that lovely shiny worm?
It's not lovely at all, but trouble brewing. The grease has departed the actual contact area of the worm wheel to the worm, easily seen here. Where the grease remains does nothing, no contact, no lubrication.
Scoop it out, degum the bearing surfaces, re-assemble, and oil it. Periodically oil again as maintenance is a requirement not an option, especially on older mechs.
BTW, new mechs and that silly lithium grease are not a solution. Open one up and see where the white stuff is. It ain't where you want it; its where it can squirt out and not be bothered just like any other grease. No warmth, no flow, no use.
The lesson here? Maintain your mechanics and periodically check, clean, and re-oil them. Grease does not mean no-maintenance required. If anything, it means the opposite.
