Do Filters Have a Limited Lifespan?

[#1]

I had a rising numbers of error seconds which was no problem until it made things grind to nearly a halt one day. I changed the filter and the error seconds stopped. After a couple of months they rose again.
Not enough to effect anything but as an experiment I changed the filter again. I'm now a month or so on this filter and so far it's only registered a couple error seconds.
So is their effective lifespan limited? Meaning do they degrade over time or is this all coincidental?
Of course I could put one of the old filters in and see if the errors start to rack up again.

[#2]

Filters will degrade if they contain commercial grade electrolytic capacitors, and that duration will be determined mainly by temperature but also to a lesser extent the level of DC voltage across the capacitor.  Even then, if the electrolytic devices have been adequately de-rated (i.e. used well within their design limits) then it should be possible to get 10 to 15 years life in a domestic environment.
If the filter only contains 'solid' capacitors then the lifetime should be considerably longer.
So as with all things, the lifetime depends on the quality of the filter and it's components !

[#3]

The above is true to some extent but an electrolytic capacitor should last at least 5+ years in the environment the filters are used.
I suspect spikes on the line cause more damage than age / temperature etc. These can rapidly kill a capacitor.
I used to work at an electronics store 20+ years ago - every time we had a thunderstorm you could guarantee at least 10 telephones under warranty would be returned over the next couple of days as totally dead.

[#4]

So reading between the lines the first (couple of years old) filter was probably expiring but the second filters error seconds (that wasn't enough to effect performance) was most likely just a coincidence.
Nothing to really worry about then.

[#5]

It might be worth seeing if you can match your filter to the pictures here - http://www.adslnation.com/support/filters.php
and see whether it was a good design in the first place.
That list is probably a good start for choosing a spare or replacement filter anyway, and don't go below 4-star ratings !. 

[#6]

Thanks for the link. I'll use that page for future reference.
My filters are just the ones that came in the routers box. I assume those are just the basic should work most of the time type.