The only time I have seen something like that is when I took the whole rear cell off the back of my 360mm tele-xenar. It looks like a major lens issue. Like others have said it could be there is a washer/spacer missing, maybe someone has combined cells from two different lenses for some reason. It really needs to be in the hands of someone skilled in lens repair or you need to compare it to another example of the same lens, unless of course it is simply badly assembled in some obvious way.
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