Redcat tornado Differential
 

Does anyone know if there is a metal replacement for part# 02039 diff cup? Or a fancy trick to stop the metal center pin from breaking through the plastic guides?

Sounds to me that Redcat should have used a differential with four planet gears (Redcat calls them diff pinions) instead of just the two in the Volcano/Tornado platforms. I don't know of any metal diff housings to replace the Tornado's #02039.

Elaborating on post above. Some of the lower priced RCs will skimp on parts to bring down overall cost. During average use with moderate powered electronics, things hold up for a good amount of time. What is a good amount of time you ask? All depends on your trigger finger, driving style, temperatures, etc.

The Tornado/Volcano diff housing only provides a slot/groove for one set of (two) planet gears to apply forces on the sun gears. Nothing wrong with this...usually. It's just that when a person gets comfortable with stock power, then they put better batteries and/or high powered motor into their RC, the weak points begin to show up.
https://cimg4.ibsrv.net/gimg/www.rcu...ea544f748f.jpg
More durable designs (like pictured below) will have a differential with two sets of (four) planet gears to evenly distribute the forces on the sun gears...more cross pins, more planet gears = more power handling capability. There is always exceptions to this as well. The quality of the materials has to be taken into consideration.
https://cimg1.ibsrv.net/gimg/www.rcu...a036977c08.jpg

More durable diff will have 2 cross pins and 4 planet gears.