Mine is number 12 006 316. Just a tiny bit older than your's! The car build date is 9/92.
The 4.2 blocks went open deck starting with 12 010 516 which is about March or April 93. I think that is when we got the plastic tubes too but I haven't been able to confirm it yet.

For reference, 5.0 blocks went open deck starting with number 12 008 761 with numbers 820 and 821 supposedly reverting back to closed decks for some reason.
Regards, Eric

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