MIKSMIF

hello everybody, i am quite new to rc truggys, i recently purchashed an absima assassin 6s from modelsport for £349.00... i do like it for the price, its strong and quite fast, all the other 6s truggys, buggys etc were £500+.. i dont think the shock springs are strong enough , they are an awkward size to replace : 20mm x 70mm i have tried to upgrade them but i cannot find a 20mm spring... Also could somebody please post how to change the pinon please, i tried but could not do it... regards mick.