Canon

[Sky Shadow]

In the G1 comics, when the Autobot Classic Pretenders and Rescue Patrol found Primus; it's a technorganic core - even with water leading toward the centre (which Seawatch happily exploits when he takes out Bludgeon )

Didn't Blaster say that wasn't actually water on the letters page?

Unless a writer tried to explain its existence, or tried to explain how it couldn't have existed in the first place, I don't see how or why some fans make such a big deal about it, or even claim that Cybertron shouldn't have an atmosphere or liquids at any time.

We know that water is rare on Cybertron in the Marvel TFU, because Octane knew that "thousands of vorns ago during an outbreak on Cybertron, a rare chemical was found" and Ratbat claimed that water was "a chemical so rare that its very existence is suspect!" (Not really that suspect, since Ratbat had used lots of it in his lamest plot ever - the Car Wash Of Doom.) But also not so rare that Bumblebee and Ironhide explicitly knew what water is in their expositions in #1.