Mechanical Failure - I'm Still Learning

In yet another plot twist, the EV Duster has suffered a mechanical failure. I was working on testing a throttle limitation circuit to keep the car from lurching so much in reverse. I was trying different resistor values and test driving the car forward then reverse in the driveway when something in the driveline snapped. Upon inspection I discovered that the weld holding the machined clutch disk center to the Lovejoy motor coupling broke.
Well it didn't actually break. It just separated from the Lovejoy coupling. I was quick to blame my amateur welding skills for this failure. However, I have discovered that the failure is much more than that.

Doing some investigation, I have learned that the coupling is made of "sintered' iron. After reading up on sintered iron and calling the Lovejoy factory, I have learned that sintered iron cannot be welded. I guess I was lucky that my weld held as long as it did - perhaps a tribute to my superior welding skills :).

So this is a "design" problem which I am going to have to re-think. The Lovejoy factory told me that a steel version of the coupling "may" be available but at about 5 times the cost. That is prohibitive at this point. Apparently the sintered coupling can be drilled and tapped, so maybe I can fabricate a splined clutch disk center that I can bolt to the coupling. I'll have to think about this a while.