SD - I have heard that advice too. Do the mechanical fixtures offer a way for the water to exit and oxygen to enter? The mechanical one on my forestay looks capable of trapping water. I suppose it might have the advantage that it could be reopened and inspected (?)
I can see that the lower swaged connections are a water trap, but under the sun's heat, I guess there may be a bit of evaporation and air entry. A rigger I asked, said basically, until strands start breaking (in life or on a test rig), its very difficult to judge the residual strength.
Some insurance companies are demanding (variously) replacement after 5 or 10 years. I suppose that is to reduce their risk to breakages.