HOLY CRAP! I printed the parts more solid this time and twice as big than the first shot but still with 0,1 mm crack only: Two hours this time for engineering and printing. First step "Knack!" I went to the living room and said to my wife: "The hour of thruth!" before the second step. "Show it to me." she answered. I with throbbing put the second part to the connector and pressed them together. Again a hard and dry "Knack!" "This sound was really solid!" she said. And yes: It fits! No crack between the parts. Position is fine. No way to separat the two parts away from each other anymore. There is still a very small possibility to twist them against each other. But it's really marginal. WOW! I'm really surprised and really happy. I mean it was the second attempt! The connection is very, very strong. Aided by some glue it'll work perfectly. But probably I can avoid glue as well. That would lead directly to a true snap-kit. Maaaan! That's an insane success.