Canon

[Hursticon]

Or was it just another case of G1 story-telling not being hindered by details?

I'd say this initially.
It was never explained in G1, no, but I believe that it has since been explained away as simply being a random mutation in his spark... That or sheer determination and will power.

[Sky Shadow]

Was it ever stated in G1 exactly why his spark is inextinguishable?

Because he still had a toy on the shelves and Galvatron had inconveniently killed him.

Sparks weren't even invented until Beast Wars, so he didn't have an "indestructible spark", he just - understandably - happens to be a ghost in a story where Octane found a Decepticon Crypt and then the ghost plot point was used again in Ghost In The Machine.

[Verno]

Yeah, so they just did it then, and nothing has been retconned since to make it make a little more sense thus far.

Anyone care to put forward an idea as to why his spark is immortal?

[Hursticon]

Anyone care to put forward an idea as to why his spark is immortal?

Umm...

a random mutation in his spark... That or sheer determination and will power.

Hehe...

I like to think of the Spark as the one and only Biological/Organic element to a Cybertronian Automaton.

[Sky Shadow]

Yeah, so they just did it then, and nothing has been retconned since to make it make a little more sense thus far.

Anyone care to put forward an idea as to why his spark is immortal?

It was canonically explained in the comic that came with Masterpiece Ghost Starscream. When Starscream died in Transformers: The Movie, he ended up in Limbo with seven other dead Starscreams from other continuities (including Marvel Comics Underbase Starscream after he was killed in US#50). They all worked together using all their scientific skills and relentlessness to create some crystal soul MacGuffins to bring themselves back to life. Then they fought over the crystals because they each wanted to come back to life and ended up merging together into an indestructible spark ghost.

The comic used to be on this page, but now all I get is thumbnails that become a "Security Violation" when I try to view the full images.

[Sky Shadow]

I found some scans of the Japanese. I'll use my extensive linguistic expertise to translate the relevant pages:

"Here's a hint"

"That's the last time I ask if someone's Megatron. Oh crap, I'm dead."

"Who are you attractive folks?"

"Let's make the best of a bad situation and pool our collective genius to return to the land of the living!"

"Truce over. Yoink!" "What? Get him!"

"Om nom nom"

"Bwahaha! I'm bac... Oh, crap, I'm a ghost. Oh well, I'll just haunt this aircraft carrier."

And he was dead happily ever after.

[Hursticon]

LOL - That's as good a translation that I'll ever need.

[GoktimusPrime]

In the G1 comics, Starscream absorbed the entire Underbase -- and even after his body was destroyed, he continued to exist as an undead zombie.

His remains were later rebuilt by Ratchet into Pretender Starscream. In G2 Starscream did use the Matrix to mutate and combine himself with Warworld. So I guess it's possible that the absorption of the Underbase and the Matrix may have mutated his Spark rendering it indestructible.

Sparks weren't even invented until Beast Wars, so he didn't have an "indestructible spark",

Well, the term "Spark" wasn't coined or definitively defined until Beast Wars. Although G1 did have similar (albeit more ambiguous) concepts of a Transformer's 'soul' -- the G1 comics called it "life essence" and the G1 comics once referred to it as the "laser core." But G1 and G2 certainly never established Starscream as having an indestructible life essence or laser core.

I found some scans of the Japanese. I'll use my extensive linguistic expertise to translate the relevant pages

Your extensive linguist expertise has somehow transformed the Japanese text into Chinese!

[Verno]

Whats an 'Underbase'?

[LordCyrusOmega]

Yeah, so they just did it then, and nothing has been retconned since to make it make a little more sense thus far.

Anyone care to put forward an idea as to why his spark is immortal?

I always put it down to him being destroyed so quickly that his spark just didn't catch on. As always read my tag.