my uneducated guess is the same as peter's more educated guess.
the screws are the wrong length and obstruct the mechanism that
separates the groups that soften the image. maybe it was done this way
on purpose because the mechanism was "loose" and defocused to soft
all the time by itself, especially when s/he wanted to image to be stopped down and sharp ...

i think jim galli used this same lens to shoot his now famous cowboy wedding ..
maybe he has disassembled his lens and knows what size the screws should be ..
or can suggest a remedy for your problem.