Is it known what they fell out over?
There are a few threads about it on here, in the ‘Characters & Actors’ section of the OT Index, and oojason covered some of it in his George Lucas: Unreliable Narrator & Time Travelling Revisionist… thread.
There is also a ton of information online, though much of it without the journalist in question admitting it was NOT David Prowse who was leaking information on the film to him.
The 2015 ‘I Am Your Father’ documentary is very much worth a viewing for more information too 👍