The circuit detailed here
http://www.vintage-radio.com/project...-reformer.html is useful not only at reforming, but also measuring leakage levels.
If capacitors like this don't reform to show very low leakage, then its time to replace them.
If they are showing such wildly varying capacitance measurements, then that could suggest there is excessive leakage. Leakage adds parallel and series resistance to the capacitor, and this trips up a multimeter or analysers method of measuring capacitance. I cant remember what that method is now, but I guess you're applying a voltage to the capacitor and its taking longer to become charged due to the added resistance...
EDIT: Actually thinking about it, some leakage doesnt show until higher voltages are applied, so emphasis on the "COULD" there. The best solution IMO is to build that leakage / reformer circuit. I use it on such capacitors when powering up a new piece for the first time. I think the likelihood of them reforming and being usable is much greater with that than just applying limited power via a lamp limiter, or lower voltage from a variac. They need something close to working voltage to reform, but in a current controlled way
Adam