I'm working on an old sample and hold circuit, using the NE5537 and 47nF polystyrene capacitors. I messed up by washing it in IPA, to remove the flux and it doesn't work properly any more. I know it's the capacitors, even though they measure good, on the bench, because I moved them from another junk board and it works. I believe some of the solvent leached into them, weakening the dielectric, causing the leackage current to drastically rise.
I've still got other boards to refurbish. Would polypropylene do?