I guess this is one topic for which one will find a range of opinions.
In the operation for which I work, the direction is very clear (I give it) -
If the pilot is not happy with something then he/she should write it up in the Log on the basis that that document is the pilot-to-maintainer-to-pilot's serviceability communication tool.
I don't care if the item actually is OK (ie the pilot has made a mistake in assessment - who cares - that's not the imperative) or busted, I just want the information to be fed back to the floor. [Pilots fly it, maintainers fix it and that has to be kept in mind throughout].
That way the maintainer gets the story, can investigate (including ringing the pilot to discuss what the pilot though he/she saw), and either fix it or write it off serviceable if there is nothing found and all the relevant AMM tests and checks are satisfactory.
If we have a concern that we are faced with an intermittent, deteriorating item, then we put words to indicate that we want the flightcrews to keep an eye on the previously reported problem. In general, this might be done several times for a given problem until it deteriorates sufficiently for the investigation to find something to point to where the problem actually is located. The caveat is that all the checks and test show no problem and this is sacrosanct .. ie, we don't permit the report to be written off with any hard indications of a problem ... those things are pursued until they are found and fixed.
The particular fleet is heavily electronic and, as we all accept, electronic gremlins can be more than a bit difficult to catch until they become slow enough for the maintainer to spot them before they can get back into their hiding spots. Typically something which takes a while to transit from being very intermittent through to a hard failure often can't be found easily.
Two instances come to mind for example - years ago, we had an electrical problem in the 727 sim (including some smoke etc) and it took the techs the best part of 2-3 shifts to track it down and fix it. On the present fleet, an intermittent looming short took 4 manweeks to find and then ten minutes to fix.
In this new political climate, aircraft systems were either black (failed) or white (working), and we pretended that the grey (intermittent) never happened.
Until you get into court after the accident and the barristers have all the time in the world to demonstrate that the maintenance practices were shonky .. just not worth the corporate and individual risk, I suggest.
In this brave new world, the grey failure has either to be rectified (when engineering still does not know what to rectify) or signed off as fully working, even when every sentient being in aviation knows it will fail again on the next flight.
Precisely and this is only acceptable if you have some rigid checks and balances to preclude Parker Rectification Syndrome. Whatever those checks and balances may be, the system needs some way to address progressively failing systems or components .. the maintainer sometimes just cannot find the fault despite the best of efforts and intentions. One just needs to be able to allow the condition to deteriorate to the point where it can be found.
New management and the CAA want us to lie and cover it up. I think it is safer to tell the truth about the grey item, and let everyone know about it.
Probably not for me to comment on the first item but the second seems to be the sensible way to go, subject to sufficient checks and balances to avoid sending out a known U/S other than via MEL or similar process.
Methodology b. is less legal but more honest - and would have prevented an accident.
I suggest that there is no regulatory problem if all the prescribed checks and tests came up good. The fact that we suspect there is a progressive failure at work is not the problem. Provided that all this is documented in the Tech Log then the maintenance system can rely on the pilot's reviewing the recent history prior to flight (all pilots do this, don't they ?)