I'm not sure if my comments will help but I myself have used both the Clarity faceplate and the ADSL Nation faceplate at different times, over a period of 5 - 7 years, and I came to the conclusion just a few years ago that the Clarity faceplate filter was more electrically robust than the ADSL Nation one, and so opted to use the Clarity. I've subsequently used the Clarity, which uses a filter design that's quite different to the ADSL Nation, for some years now without a single problem. I started off with it when I was on ADSL Max; it's currently in use on VDSL, and gives truly excellent results.
Way back, I acquired the ADSL Nation first of all. Before ever putting it, or later the Clarity, into use I took it apart to find out what sort of filtering was incorporated and was quite surprised when I found that the ADSL Nation used transistors in amongst the chokes and capacitors. So, as a retired electronics professional, I felt that this was rather risky on the reliability front, given that the line could be subject to voltage surges. Even though the transistors may have been spec'd at over 50v Vce each, this may still not have been good enough to cope with perhaps an odd, very high transient. So, I decided to stop using the ADSL Nation, and I bought and fitted a Clarity instead, which employs a totally passive filter (and therefore no transistors).
Now, I'm not necessarily saying that that's your problem in this instance. As has rightly been stated, capacitors can, in time, become electrically leaky. Indeed, even some might have their working voltage exceeded on occasions, which clearly won't do them much good. Another cause could be a solder joint on the little printed-circuit board that's become dry.
In your shoes, I'd continue looking for the source of the problem elsewhere first. But if that yields no result, I'd recommend you acquire and fit a Clarity faceplate filter instead. It'll give you the same sort of termination options as with the ADSL Nation. The two faceplates differ in external shape; whereas the ADSL Nation has a steep wedge-shaped upper section, the Clarity's is bullnosed. I seem to recall that the Clarity cost much the same as the ADSL Nation but was marketed by just one particular e-retailer here in the UK (curiously, with the URL 'clarity.it' but despatched from Scotland), but I'm not sure whether they're still in business; you'd need to google around for one.
Postscript: I just tried googling for it myself, without success, but have just found this, which looks remarkably like the Clarity one and in all probability is the self same one:
Edited by meditator (Fri 16-Jun-17 11:44:38)