I suspect our star system has been visited by machine intelligence from outside the Solar System about once every 10 million years. There should be lots of ET's junk laying about if we only knew where to look and what to look for. I suspect some of those metal "asteroids" that are under 1 km. in diameter might not really be asteroids.

What you say is why I believe there are no technological ETs anywhere and there never have been any. Machine intelligences capable of surviving an interstellar journey would be robust. They should have filled every corner of the galaxy several times over by now, no matter how slow their starships were or how many times an expedition journey failed.

Another place to look for ETI is in our own DNA. Wouldn't it be cute if someone did a careful examination on our own genetic sequence and discovered a designer's logo and serial number. It wouldn't necessarily be with human beings that our world was seeded with by ET. One could speculate that a machine intelligence came by during the Cretaceous Period, concluded that our Earth was stuck in a biological dead end and deliberately perturbed an asteroid to wipe the slate clean. The same machine intelligence then picked up some of the more robust survivors and reprogrammed their DNA to fast track evolve into intelligent tool using apes.

Sagan took this idea one step further speculating in Sci-Fi that the constructors of this universe embedded codes in physical constants like pi.
I don't buy the premise that one coud twiddle DNA once, then leave it alone and really expect an end result 60 Myr later or even 2 Myr later. Too much chaos theory and random chance in subsequent evolution.