The dust cap was
"rust-welded" (I forget the term) stuck in the left arm due to galvanic corrosion. First the hex rounded. So I drilled two holes into the cap to turn it, but it’s still not moving. I manage to remove the bb from the frame with the left arm still attached. Now a hammer and punch on the cap — this thing will not budge. New strategy is to sacrifice the arm for the bb. I hack two cuts through the bolt end of the arm and extract the remains of the cap. Got the bolt loosened. Now how to remove the arm from the spindle? I hammer at the loosened bolt — nope. So then I hammer at it with the spindle resting on on a piece of wood (lateral force) and it starts to come free.
Turns out the spindle has a couple pits in it.
PS: Though I wasn’t specific, I was initially thinking
mechanical disasters. Note that below there are reports of personal injuries.