[Yaesu] filter degradation

[Chris Codella, W2PA]

I have an FT-1000D that I bought 14 years ago; it has all the original 
filters.  Recently - within the past year - I've noticed a rise or 
degradation in the floor level of the 250Hz filter.  During a contest I 
can now faintly hear CW signals that are significantly far outside the 
filter's passband.  It's more an annoyance than an impediment to 
operating as it doesn't seem to affect the AGC.

Have any of you noticed filter degradation with age of these things?  
Any explanation other than a problem with the filter itself.  I'd like 
to diagnose this fully before buying a replacement.  Is it possible that 
one of the two cascaded filters has failed entirely and I'm hearing the 
affect of losing one?  Any other wisdom from the assembled Yaesu multitude?

Tnx, 73,
Chris, W2PA