I would make dang sure the new tumbler is installed correctly, and the locking ring is seated all the way down first. One thing I learned is to use some needle nose pliars to turn the ring. It would only go so far with my fingers. This does scratch it a little, but is not very noticable.

If you cannot get the key to turn, then that means you cannot unscrew the locking ring to remove the tumbler again. That also means that if you do need to replace the housing then you will need to drill out the pin to release the housing from the steering column.

And yes, that is the correct picture of the next suspect after you are sure of the above info.

__________________
----Adam

1985 300SD 322,000