This little current source has been acting up for some time, occasionally it would produce lower current with tremendous amounts of noise, a little mechanical persuasion would usually fix it but now I have enough of it and had a proper look at it.
From the outside I could narrow it down to the external/internal v-ref switch on the back.
After opening up the digistant I spotted the culprit, can you?
It have been like this for forty years.
Apart from the defect and one of the resistors on the second decade being out of spec, it is a handy little thing.
Pics attached for your entertainment.