The truth is that there is an appropriate use for every fore mentioned product.Actually with the new fiber composite gaskets that have silicone outlines "all the diesel engine manufacturers us them'" sometimes only a bit of Permatex hightack is necessary, just to hold them in place for assembly.RTV silicone is a necessity in some cases but must be used sparingly and only where it can't cause damage by migrating to an area causing a problem.The good lord only knows how many gasoline engines are nearly gasket free because of the stuff,to say nothing of heavy duty gear drivelines in trucks,loaders etc.The same holds true for teflon tape,used properly by a professional it is fine for most applications, air,water,vacuum,etc, not involving lube oil. The trick with teflon tape is to NEVER use it on the first two lead threads when assembling,if you do... expect contamination.
When sealing pipe threads involving fuel or motor oil,I have found Rector Seal pipe dope to be impervious.On most seawater applications,"pump covers,gear coolers, heat exchangers,"I use vellumoid gaskets and #2 Permatex or 2 coats of Permatex hightack,otherwise a year or two later you will see the salt leaking by.For sealing bolt threads that enter waterways on engine blocks RTV is the ticket,also a very good substitute for locktite in areas prone to vibration.Once again,when assembling a transmission companion flange,apply it evenly and lightly to the splined area,preventing passive oil migration behind the nut and flat washer,the same goes for the intersecting angles between blocks and oil pans.
There aren't many bad sealants,just bad use of them.
