Measuring old capacitors - what could cause large deviations?
I have heard of low grade electrolytic caps having a -0% to +100% tolerance but yours appears to be +163%. I'm not greatly surprised. When you design in an elco the main parameter is the minimum capacitance,  you know the maximum will be a lot more.

When an elco hasn't been used for a several years you are advised to reform it. You could give that a try, but to be honest I would expect reforming to increase it s capacitance rather than reduce it! However, reforming may reduce the leakage current, and perhaps that is confusing your measurement.

To reform your 6.4V elco connect it to a 5V supply through a 10k resistor for about 10 minutes. Then try measuring its capacitance again.