A Metallurgist's Doubts About Self-Replicating Probes

An interesting related discussion:

Will We Ever Find Alien Civilizations? https://news.ycombinator.com/item?id=48860916

I listened to the podcast version (and was awake for much of it). There was talk of self-replication probes and if there is intelligent life out there where are the probes swarming all over the place.

In addition to the probes out to colonize the galaxy, many of these problems are likely (it seams) to spell trouble for any space economy. It would be interesting to solve some of the problems (and see real world [solar system] use) of the technologies / techniques.