Plenty of very good points here already.
Many years ago, I had the pleasure of working with a pilot who believed he possessed exceptional and unquestionable mechanical abilities. He omitted to explain them to anyone when he was hired as a pilot, so as Chief Engineer I was not aware of these incredible skills.
One day, one of his activities was brought to my attention. He had accomplished something totally at odds with basic operating regulations, maintenance manuals, safety and common sense not to mention company operating procedure.
I contacted him immediately and asked him about what I had heard. He admitted it was true, was legal and that it was none of my business. In response, I politely advised him that ALL maintenance activities of our company were the directly delegated responsibility of myself, and that if he believed his stated position to be true, he now worked directly under my control and that I would now control his fate. If he elected to resume the responsibilites of a pilot and thus remain under the control of the Chief Pilot, that was also completely acceptable to me, but he would be one or the other.
We resolved the maintnenance issues. He stayed as a pilot and actually became a very compotent and valued member of our team.
The moral to this, is that failing to remedy a situation like this implies complicity for all others involved.
I am not talking about actions to get you out of a life or death situation, or looking to see if you can determine the source of a problem, or performing routine operational inspection and upkeep; but performing maintenance actions that you do not have the legal authority to perform. How can you define this position - generally when you are undertaking actions affecting the integrity of the aircraft or system and not making an appropriate log-book entry, because you can''t.
All you have to do is consider how this action would bear review in a Court of Law, where you will explain what you know, under oath, to a jury of your peers, in the presence of family members and colleagues. Want to know what this feels like - just ask anyone who has had the misfortune to go through it - I have never met anyone yet who enjoyed it or would want to do it a second time.
Best means to remedy this, is to talk to the Engineer responsible for Airwothiness. Whoever signed the last inspection, is unlikely to be happy that undocumented actions are being undertaken, that will probably be connected to him, should they lead to a problem. Likewise, the next Engineer inspecting the aircraft may be interested in looking at items that have been disturbed (but not documented) and may ultimately be connected to him.
Next step the Chief Engineer, then Chief Pilot, and up.
If all else fails, put it in writing. There are not too many companies that will fail to act on something like this in the modern litigious world.
Good managers and good companies can (and must) resolve issues of this nature before they escalate. They can be accomplished easily and thoroughly, whilst positively modifying the behaviour of the individual to everyone''s benefit.
Let us know how it goes.