oiler..... I can see steam condensate drops on the inner lubricator quartz tube.....but cannot see any steam oil in the tube

Your Niggle lubricator has the adjustable needle valve @ the top to meter the oil flow.........essentially to conserve expensive steam oil

Without any real experience in understanding the method of determining a nominal flow......I chose the fixed orifice version...& will rely on the calculations by Winfried.....

Steam oil should not breakdown with age

.....but considering the cost of our engines

we should ensure the correct quantity of oil is getting into the engine etc

My ACS Engineering components [boiler, regulator de-oiler etc] ............ were purchased in 2005 - ACS Engineering [Scotland] has since ceased trading.....................his home page was removed from the WEB many years ago
I did a GOOGLE search on
MMR01 R/C Rotary Slide Valve Regulator ...& found another WEB site where you had posted similar images ....then Q&A on the same issue
Each to his own......but if I had an issue with the lubricator or the steam regulator leaking or not working I would take it up with the manufacturer.........Derek