Thank you @peci1 for explanation.
Even if I understand little about how Multi-level cells are working…
Checked my favored online electronic parts dealer for the needed pieces and will order them. Just in case.
You forgot that all logs (there could be many of them) are written to eMMC as well, if not redirected 
Indeed. Have a look at /var/log/messages. This is continuously written to and rotated on the eMMC. It will be automatically moved to an installed SSD.
Not automatically - you have to set it either manually or in reForis
All logging on my Omnia is default. No custom settings are made.
-rw------- 1 root root 632.4K Sep 7 20:00 messages
-rw------- 1 root root 1.0M Sep 5 23:12 messages.1
-rw------- 1 root root 21.4K Sep 3 00:12 messages.2.gz
-rw------- 1 root root 54.2K Sep 1 13:12 messages.3.gz
-rw------- 1 root root 14.8K Aug 27 00:12 messages.4.gz
I would say, this files alone cannot bring the eMMC to an end. Maybe there is to add the DNS resolver cache, because I disabled the “use forwarding”. And schnapps writes data every week.
As mentioned in this topic eMMC - live span, health monitoring - #9 by cynerd - Omnia HW problems - Turris forum
Flash memory in TO is (up to my knowledge) SK hynix eMMC4.5 which manufacturer specifies, for density of 4GB, 2.4TB total bytes written before EOL.
I don’t know when or what could write that much data. Let’s even say 1TB in 6 years.
What I said before. I use this Omnia without extra packages.
That’s why I don’t added an extra mSATA card in it.
That’s not right. By default, /var is symlinked to /tmp, which is by default kept only in RAM. The only persistent folder where some data may be written periodically, is /srv. And by default, no apps write here (not sure about the resolver, though). By default, you even lose DHCP lease assignments by rebooting.
Resolver only writes to tmpfs.
/srv I never used and yes after reboot all the log data is gone. So must be in the RAM only.
Then I don’t unterstand from what the eMMC dies.
Or can it just because of the age/runtime of the device?
Of you don’t use “server-software”, then the only activities degrading your eMMC are system upgrades and usage of schnapps.
Then, that must probably be the cause for downgrading my eMMC over the years.
What I don’t understand - my wear out-level is 10-20% with two Indiegogo-TOs, that are running round the clock and have been updated with ~90% of all the upgrades that were handed out until now.
So either I have very good flash or yours is part of a bad batch… 
eMMC could be worn out by leaving all logs etc writing to it. One should redirect logs etc to USB or SSD
Never did that in my environment. And if I remember correctly those logs all write to /tmp, which means RAM, since 2 or 3 years by now.
There might be for sure nonstandard apps installed, that behave differently and thus harm the eMMC.
Search for eMMC on Forum…