The carrier-shaft bushing on the left and right of the printhead assembly
were broken on our ImageWriter II; we replaced both items. Now, the left
side is too snug when the right side is adjusted properly, and the right
side has too much of a gap when the left side is adjusted properly.
Other than playing around with more shim kits, you probably are looking at
a bent carrier shaft. If the shaft is straight, then you should be able to
adjust the printer with the shim kits; all but the very worst gap problems
can be solved this way.