really poor casing problem?

[vrooom]

Hi, I ordered stuff for my team c buggy, this is the 2nd time i across a very poor casing problem on metal work on diff gears.

When i ordered my team tm2 v2 kit, the diff 16t gear that came with it has poor cast, leaving bits of lump of metal between the teeths, even with half teeth missing.

recently i ordered diffs kit for my buggy, the part no TS4039, one of big gear has no teeth, and few chucks missing from same gear.

Why so poor casing? Has anyone came across anything like this?

Which is shame, rest of the car's quality is top notch.

See the pic of old TM2 v2 diff(left) and my buggy diff(right)