I was having a problem on a certain length of track, shunter was not running smoothly and was jittery and sometimes stalling. 
I cleaned the wheels and track, seemed to be running a little better but not perfect. So I decided to buy some loco oil, oiled the wheel bearings and worm gear. Both shunters are now running perfectly smooth with no stalling or jittery motion. Also oiled the axles on my wagons. 
Bought this from eBay it’s great stuff. 

Well found Gray, I picked some up a while ago and it's surprisingly better than my old pen of loco oil.

Modern oil tech, great stuff :)

Hi. Thanks. It’s surprising what a bit of oil can do. The two shunters were bought from eBay, used but in good condition. Probably never been oiled. 
I’m running dc and they are now running really smooth, the slow speed is good. No stalling or jittering. 

These were produced from 87-91 so over 30 years old, a bit of oil worked wonders. 

New shunter oiled and lightly weathered, runs perfect. 

Those old 0-4-0 shunters take me right back to the old Triang "dock" shunter which was a must have on most layouts in black and white days ………………

Pleased you got them running sweetly.  Must keep my eyes open for that oil - I wonder if "Total" do enything that thin here in France ……………..