XRAY - Model racing cars

hi guys ,after 3 xb8s it was time for a new one again so along came the tq
nice looking kit the only real diff to what i was using was more front droop.anyways while building the rear shocks i used the supplied rear bodys but low and behold the front ones where tight as well so i raided the pit box for some new ones thats my first complaint..(grin).next the diffs front and rear went together a little to notchy for me but cause its new i let it go ..
first race with it usual set up probs as expected nothing working the same but starting to tweak hear and there then a clutch bell bearing failure within 10 mins of use scrapped the bell as well..ok all fixed off we go again then the centre diff large bevel gear decided to spit off its teeth locking up the diff not a happy camper in 3 seasons with xray never had a diff failure..sorted that and finished the day off.......got haome stripped out the front and rear diff ..the diff oil inside totaly black and gears still notchy so i replace both larger bevel gears again out of the pit box on each diff and diffs now smooth again im wondering has there been a batch fault, so a new car has had 3 sets of diff gears and front shock bodies in less that 20 mins run time ....has only one else had probs with the diffs either breaking being notchy or turning the oil black(which is a wear indications in my book)

Still building the drive train and find the rear diff sticking, advice is diff housing ng. ordered new. Its my first xb8, been running H8 and Hn. Might put in three spider diffs instead. What do you think? oh, best kit i've ever built.