I think it is a big advantage if we normally use online sources that everyone in the discussion can freely consult. It can be especially confusing when people quote out of context, and don't give a link providing the rest of the passage. Context can sometimes make all the difference.
I can't give a link to an online version of MTW "Gravitation" but I do have this article from the Institute of Physics 1993 Reports on Progress in Physics
For what I think is an extremely clear discussion of the "hole argument" see pages 801 and 802 of Norton's RPP article.
For a discussion of Einstein's 1915 statement of ontology (space and time not physically real) see page 804.
Norton is clearly an expert in these questions. It's not just textbook-style coverage--an IOP review like this has a different aim, more along the lines of "definitive monograph" that takes the time to lay out difficult issues carefully.
I might not necessarily agree
with everything J.D. Norton says (for sure!) but I have to acknowledge his presumed expertise and balanced judgment. Also he highlights controversy and presents both sides where he finds disagreement. (There are certainly statements in the article which, if isolated and quoted out of context, I would have to suppress my urge to quarrel with. Presenting both sides is part of a scholar's job.)
John Stachel is another expert of like caliber. We might find something online by him.
Anyway hopefully this J.D. Norton article will be of use.