The problem is simplified at the picture of the .jbeam. Sorry, too lazy to write and apart from this you can see the file for if it is scripted badly you can tell me. Creating a new body, the engine slot (custom) doesn't show. Thank you very much!
Yes, and I tried a long name, short name, and still happens the same --- Post updated --- Well, I thought I didn't clear cache and I tried and the slot appeared, I don't know why but it worked. Thank you by the way @Ai'Torror!
Your new slot will not show up in the slots unless everything is named properly. Another reason that your slots will not is if it is empty.
It appeared with what it should list, I took a deep look into names, changing names and all that stuff and I didn't understand why, but now it's solved. Thanks!