I also have a box full of these, and when I checked them, most were leaking, not just ua with volts attached but indications using an ohmmeter.  The block with the two mounting holes had a higher failure than the flat ones.   Still, being 80+ years old, many still hung in there.  When I was solving the last issues in my TCS station, the key to getting rated power out was finding many of these caps leaking, some only a little bit, megohms, but enough to make a 20 watt difference in output.

Charlie, W4MEC in NC