I have started building a 502x and noticed that it was hard to install the forward top deck, and when it was installed, there was a noticeable tweak.
I'm not saying this will help reduce your front gearbox breakages, as I do not know exactly where they break, however it would not hurt as currently the top deck is putting too much stress in the g/box housing in my opinion. Also with the top deck jammed against the g/box housing, it is creating a too rigid front end and if the housing has no 'give' in it, it will just break. Where as if they were separated by just a little distance, the g/box housing would have just a little more flex and possibly reduce breakages. Anyway just my thoughts anyway, I'm liking the build so far, it looks really bling
As I was building this car, it reminded me so much of the hot bodies d4 design, and both cars seem to have weak front g/box cases.