Thanks for the ideas guys - I'll replace the center plastic mount and use longer screws and see where that takes me. I think I have everything else covered (ordered shims yesterday too).
I've been inspecting the gears now every run and they seem to be hotter than expected so I checked to make sure something wasn't binding and creating additional heat - IE: causing it to sort of do a slow-unload over the duration of a qual/main. I haven't temped them yet to get a baseline, so not sure if this is an indication of an issue or just normal. This weekend I'll have my temp gun with me. Part of my theory is the heat could be softening the plastic leading to early failure.
Tekin 1900 is running pretty cool at 15/45 on 4S, but I might see if a 16T on our medium to large track would take temps down a bit (to see if it's over spinning).
Seems like a aluminum center diff upright would help with stripping, and maybe even some heat dissipation (heat sink). Like they have for the TEN-SCTE:
http://www.kingheads.com/product_inf...8b77e7ab694fc3
Time will tell..