Hi Love the gearbox covers and the use of the Pershing gearcases (where did you find the pershing gearcases),
The Tamtoy gears have a few of them and have modified them ,If you check them out they suffer from poor tolerances ,as usual from China (good ideas spoilt by slap happy tolerances),The fix is quite easy 3mm reamer and 3mm silversteel,reamall the bushes and gears 3mm then change the shaftswith the 3mm silversteel,takes about 40mins,gears run better quiter no backlash.

regards pete