Actually I found suitable single caps on Farnell (Rubycon CXW), the series caps was a temporary fix just to check it was the only problem
I've read the same advice about adding bleeder resistors to series caps while looking for replacements.
What's your opinion on replacing all the other electrolytics ? It wouldn't be that expensive, like 30 euros total for decent quality components. But should I do it ? They're probably not part of the precision equation, or are they ? But it would imply soldering all over the place, near the reference etc.
Also what are my options to check the calibrator or even adjust it ? It's a hobby so paying thousands of dollars for a cal lab is not an option and I don't have anything nearly that accurate...