No offence, but what major German companies write in fond belief that they are writing English, often isn't.
I have seen horrendous English on dozens and dozens of websites of major German companies.
How many of us have had to argue with them that 'imprint' is NOT a correct translation of Impressum?
IMO, 'interface' is perfectly OK.
No, 'transition' doesn't strike me as appropriate.
"mechanical connection point" can work, but seems to me quite unnecessarily wordy, unless it's vital to emphasise the mechanical aspect. Even so, I wouldn't repeat it 250 times in a document, at the very least dropping 'mechanical' after the first mention.
'junction' is used in very specific contexts.