[exray]

One of the main problems is guys attempting to twist the mica caps over to see what might be written on the other side. Sometimes this is all it takes to break the seal between the casing and the lead. If you've ever looked inside to see how they are constructed you can see how the metal 'leaves' are so easily broken (or shorted) if the lead is free to twist. There ain't no going back once that happens. This is true of all of them whether paper or mica. Of course the paper ones were probably bad anyway

Best to leave them alone with the exception of those that are obviously paper because of their capacitance value or physical size.

War story...I bought a grab bag of about 100 NOS domino-style mica caps. All mica, no paper. About 25% of them were bad. Just goes to show that you can't trust them 100% but 75% is a relatively good ratio compared to paper caps.

Raleigh is right. If you're going thru all the trouble to remove them and test them then you might as well replace them. Otherwise just leave 'em be and troubleshoot later if you encounter problems.

-Bill