It's a standard Austin/Morris wiper system which dates back probably to the early fifties. The wiper motor is common to MG/Triumph/Land Rover etc. A tube runs under the dash with a spiral bound inner. (Like a posh bike brake cable). This locates into a concave profiled drive wheel at the bottom of each spindle on the bulkhead. If you remove the arms and run the wiper motor you'll see that the spindles rotate smoothly with minimal free play. The arms locate on splines and are tight, so the only slack really is in the arm to blade join - and you've already identified that. Mine seem to work surprisingly well, with no judder. I use abrasive (Rain X) glass cleaner and Rain X very frequently. The blades don't cross the screen frame at either end.
