In item #43 of this list states, as an "inside secret," that Richard Marquand was fired from Return of the Jedi and that Lucas had to take over directing duties to finish the movie. I did find indications that Lucas helped him with the FX issues, since Marquand had not worked with FX shots before, at least not extensively. I also found articles, without major support, that some think Marquand was director-in-name-only and Lucas did most of the work. Interviews tend to indicate that there was a good relationship between Lucas and Marquand.
Do we have any clear information on what was the actual relationship between Lucas and Marquand? For instance, did they work well together and was Marquand actually directing? Did he need help with FX issues due to lack of experience in that particular field?
Clear evidence and not rumors or publicity interviews would be appreciated. Any interviews that show both have the same story would help, but shallow interviews like, "Oh, he was great to work with," that lack supporting anecdotes or support would not be useful.