thought it was time for an update
the bike is now up to 2200 miles travelled and has had the following replaced over the last 3 weeks due to wear and tear;
both drive chains (motor and pedal) both were pretty stretched
front sprocket (now Shimano 48tooth steel) as the last alloy one was really soft and the teeth wore quickly-time will tell if steel is more durable
rear sprocket (13t from a Brompton, as before) no wear noticed
replaced the stock rear axle nuts on the Nexus rear hub with North Shore Billet allen head nuts (way better)
the gearbox was pulled down; the Chinese bearings in the planetary gears were replaced with quality SKF (easy as they are skate board size) these were loctited in turned 180 degrees and deburred. As before gear oil was used and the box was sealed with loctite flange sealant.
this has worked well; however......
there does appear to be vibration comming through the right side pedal at certain motor speeds, with a 'scuffing noise from the gears in the box'
I will run it for a while and see if it settle down...maybe needs more gear oil