What you say reveals one of the major problems in aircraft maintenance. The "guy in the office" that writes the manual is intimately aware of just how things are maintained and the reasons behind the procedures. He writes procedures that he expects people to follow but of course there is always room for improvement. (Bear with me...this is relevant to the topic)
In the field, the service guys often make it up as they go along instead of reading the procedure. The majority of techs I've encountered try to fix things on their own using their "common sense" before referring to the manual and when they come across an area that may require improvement, they simply do their own thing and don't bother informing the people responsible for updating the manual. And then you wonder why the "guy in the office" may not be aware of some obscure in-service anomaly??
One real life example I can offer has to do with de-ice boots. For those of you that don’t know, every airframe component (even the rubber ones) must be electrically bonded to one another. This means that they must all conduct electricity and be electrically interconnected. Many airplanes that use rubber de-ice boots achieve this by using “conductive” rubber that has been manufactured with an additive that conducts electricity. When the de-ice boots are installed, a thin strip of black conductive cement is painted at the edge of the boot, overlapping the boot and a bare metal strip just behind it. Many older de-ice boots that are found on aircraft like the HS-748 are made with non-conductive rubber. They must be painted entirely with conductive cement on installation.
I have seen many many instances of de-ice boots being installed that are not bonded to the airframe. Some AMTs decide to use non-conducting edge sealer like PRC (a common catch-all name for a series of sealants often used in aerospace applications) Others don’t bother painting the surface of non-conducting boots. The results are premature wear of the boots due to electrical arcing and surface deterioration and excessive radio noise when flying through precipitation.
These procedures are bred from the “common sense” that most AMTs think they are born with. Even when they read the procedures in the AMM they discount them as silly or incorrect without investigating the reasons behind them.
AMTs (or whatever you call them in your part of the world) are responsible for conformity. That means they make the airplane match the type design. No more, no less. If you stray from the maintenance manual procedures, your airplane no longer conforms and your signature is useless. If the procedures have errors, it is the AMT’s duty to have them addressed and corrected either by contacting the manufacturer or the responsible airworthiness authorities. Does this happen in the real world. Not often.
Here-in lies the relevance to this thread (finally!) A lot of the misinformation comes from this “common sense" approach. I’m guilty of this on occasion as well, but I try to temper this type of information by using terms such as “I think” or “I’m not completely familiar with the system” etc. If you’re not sure of something , state it and try not to pass on information that is contrary to the AMM (or other references) unless you are prepared to back it up.