hi i have a jato too and i love it, my 1st nitro i think i had the same problem and wd 40 seemed like it worked but it just smooth out the grinding sound it didn't go away, it was the bearings in the crankshaft, there r 2 of them one in front and one in back the one in front was bad but i changed them both, you also said you tore it all down, is that just taking parts off of chassis and looking at them., i took my transmission apart 2 times before i found the problem