Godzilla's onomatopoeia

I don’t know about the legendary roar but the Toho One is officially pronounced “Gyaoooon”.

That still doesn't sound like a godzilla roar when I vocalize it. I've gotten good at mimic animal roars

Skreeeongk always sounded like one of Rodan's short cackles to me, I never understood how they got that from Godzilla's roar. The key I think is to use the Gyaooon more like a guideline and improvise the actual sounds. There's a lot of subtle noises in those long vowel parts that can't really be conveyed without a lot of confusing accent punctuation, so it's more to get you started in the right direction than a perfect copy. Like how cows go "Moo" but that doesn't do justice the actual sound, just gets you in the ballpark.

Now Gyaooon sounds like the original Godzilla's roar

Exactly, which is what that onomatopoeia was created for as far as I know. With the later Showa era I think if you really rush through the "Gy-" bit it still works just fine. Legendary's roar? Beats me, seems like the sort of noise you'd have to somehow start with a really dry throat and then end with a guttural gurgle-y thing, which I don't think is possible. :P

Perhaps for Monsterverse/Legendary Godzilla its Gryaaaaaaaaa-inuuuuuum (like a deep echoing whale)

I love that this is a topic. Thank you to all involved.

Your welcome, it just came to me when looking at youtube commits, trope pages, and other sources featuring the SKREEEONGK!

Now that I think about it Rodan's showa roar does sound more like SKREEEONGK.

Showa Ghidorah was basically bibibibibibi