That's the sort of philosophy we have ... with the only difference being that deferral requires a known U/S so is not applicable to a yet to fail gremlin situation.
With a grey snag, if all the routine tests show the system to be serviceable then I have no problem with the boys on the floor signing it off "checked serv etc" .. after all, that result defines serviceable. Especially with the electronic stuff, we have that situation arise fairly regularly .. much to the annoyance of the flightcrews. As an organisation we are doing it better as we go along .. mainly as a consequence of improving shopfloor corporate knowledge of the particular fleet's idiosyncratic behaviours .. same as for any fleet.
If, however, we suspect that there is a progressively failing scenario then that is when we consider putting in a note to the flightcrews to advise further. We also have a process whereby the flightcrew hierarchy is briefed on whatever the particular perceived problem might be.
In the ideal world some appear to be suggesting, the a/c would need to be grounded while every mm of the RA and other avionics is changed - and even then it may not be fixed.
That, of course, will never be the system purely for reasons of engineering and commercial logic ... we are in heated agreement on that point.
Unfortunately, system workability (aircraft and any other place) doesn't work in a strict black/white binary way.