silicone is good stuff, but only if the surface is prepared for it. still, there is better stuff to use than silicone

Whats the better stuff to use? Teaser ;-)

It all depends on the project... not every product is the best for every job...

How about for this job then?

if you are referring to the picture, No... the previous owner had a leak and thought that applying silicone would solve it, but it didnt. silicone is NOT the right stuff in this case because being exposed like it is, the longevity isnt there.... for a temporary fix it may help, or when used to bed an object where the sealant is not exposed and the bedded object wont move, it works fine... but it also depends on the quality of the silicone, as all silicone sealers are NOT the same.
as for the chainplate repair in the picture, im not sure a 3M product like 4000 or 5200 would have lasted long either due to the allowed movement of the chainplate because of the hole thru the deck was a bit oversized. the chainplate movement needs to be minimized so that the seal does not rupture or lose its adhesion, then a permanent seal can actually be permanent if care is taken in prepping the surfaces...