Rolfkt, your not the first guy thats happened to, when you worked the horn in the oil, did you squeeze the end to see if it was getting pliable?, Ive found with working buff horns that sometimes you have to do the rounding process with a sizer a couple 3 times, sneaking up on it pushing the sizer in a little at a time, letting it cool with the sizer in then repeat the process a little deeper each time, and them sometimes it just cracks anyway! Happened to me last week with a flat horn, had the thing pressed real nice everything was looking good, left it in the press, walked away for a couple hours, when I came back, the horn split as it cooled along the bottom curve, luckily it only cracked on the outer half of the thickness so it can be filled and fixed, still its just another step that agravates yea! sounds like you still have plenty of horn to work with yet, especially if you turn a beehive plug for the base, that will help balance the horn.
