Many of the Canon LTM lenses will come apart very easily. All that is needed is a sharp spanner to remove the rear retaining ring. Usually the optical/aperture group separates cleanly from the focusing helical.
If you can get this far into it, you may be able to find the problem yourself. Could just be that the group/s attached to the aperture mechanism on the front need to be tightened or taken off then re-threaded on. The threads on these aluminum barrels are incredibly fine and it's not improbable that a fall could have knocked the front group off by a thread.
If you're brave, I say do it yourself. If not, there's always many folks out there (and some here on RFF) who are able to fix the problem.
Good luck!
Phil Forrest
