Mumbles, you’re correct, it was an aluminum friction block.
I used my "garage" hair dryer to heat the outside of
the grip for a while, then inserted the grip on the tiller
handle, engaging the friction block. I gave it a good
twist, and if popped loose. All back together and
working good now.
I also tightened the mag plate per an old thread, putting
four little dimples in the brass ring. Chris wasn’t kidding
that it only takes a little tap on ring to tighten things up!