Who keeps the tanks of the Guard running?

The Adeptus Mechanicus step forward to fill that role.  I have a few representatives although I did miss the Tech Priests from Rogue Trader/ 2nd Ed and no longer have any of the metal ones that came later.

The spanner monkeys are led by the current plastic Enginseer.  To his left, one of my favourite figures is the Rogue Trader Squat Tech Priest equipped with the Spaceman White Dwarf's servo arm backpack.

He is backed up by two of the techno-archaeologists from the various Blackstone Fortress releases athough I did obtain one via the US release Combat Arena game during a trip in 2019.

From the Elucidian Starstriders Kill Team.

Toiling away in the background are the Servitors again ranging from Rogue Trader to Blackstone Fortress releases.

 There are more Tech Priets but they are currently residing in boxes with my Adeptus Mechanicus units and their particularly large pile of shame.  A hobby project for another millenium probably.