I've done quite a few. As I said, it's a challenge, and takes a good variety of sockets and extensions, and those under the coils are really toughest, but it can be done.
The "brown crud" on the #5 plug could be from oil, coolant contamination, a slightly rich mixture along with weak ignition, or poor compression and a cold cylinder. An injector flowing too little would tend to create a fairly white plug and too rich would tend to create a dark brown or black soot on the plug.