Hmm, never heard this before about the 515 filters. My almost 25 year
old 515 works great, just needs a little alignment in the PBT circuit.
A friend's 20 year old one is fine and dandy too..

BDK

You will be able to recognize if it happens if you start experiencing
reduced sensitivity in the SSB modes. Not a big deal to clean and repack the
filters. About an hour and a half for both the LSB and USB filters.

Pete