Thanks, Mats!
I'm working on running this version now.
I can't easily use displacements to assemble it as I want to test the disassembly mode (I'd presumably have to create several enforced displacements with custom disp-time functions, so that it first pushed the parts together and then reversed the one I want to pull out.
Therefore I've stuck with my 'as-fitted' model, and I'm now trying to find the necessary mesh size and number of steps to make it converge with larger amounts of pull-out; I've successful tested the principle with a small displacement, but it initially failed with larger movements (i.e., into the 'critical' zone!).