Hmmm,
My mid gearbox did appear to have a slight high spot when I built it. It was noticeably worse if I pinched up the screws and the motor plate bolts hard so I ended up carefully tightening all the screws and bolts in a cross pattern (like you would for a cylinder head) and backing them off a touch as soon as I felt the high spot. On rctech, I think I read somewhere that some guys were using threadlock on the motor plate and not torquing the plate down hard.
I don't know why but the mid gearbox does appear to be more critical to torque down than the rear gearbox does.
Also, make sure the idler shafts are fully inserted and pressed into the case half - from memory, I think the top one is quite tight.
As for the high spot now - it certainly doesn't appear to have affected the gearbox at all in operation and I can't detect it now so it seems to have bedded in.
Don't know what the cause is but perhaps the shape of the mid gearbox makes it more prone to warpage during post mold cooling?
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