Live Steam Pressure Gauges

[Hope Mountain Railway]

Does anyone out there have any experience of repairing/cleaning Roundhouse or similar pressure gauges? I have 3 now which have failed out of warranty. Roundhouse very good at replacing within warranty. They are expensive to be a 'consumable'. My son's new Ragleth's has also failed and will need repalcing. Have tried using the ultrasonic cleaning bath at work, but to no avail.