I read through that and didn't catch your comment the first time about the leaking...you were right!

Anyhow. For fun, I performed the Uber High Tech....."Play-Doh" test on this gap to get a better idea of thickness needed with an assembled block.

By the way this only works with ORANGE Play-Doh and no immitations will work the same!...

Almost exactly 1.0mm of gap is there per the official "Play-Doh" testing lab...(And don't tell my son about this!)

If you only want to seal, you need some softer material just about 1mm or thicker, and to bow....something thicker than 1.0mm..