Hello everyone-- I need some list experience here.....

I got a used replacement sliding door handle complete with lock & key last
week.
Thought it'd be good to have one key for all the doors, so,  change the lock
cylinder from my broken handle to the new one.
just turn  out the set screw, remove the cylinder and replace with my old
cylinder. So far so good. Disassembly easy.

Cylinder is turning nicely in the handle, locking tab is moving nicely, but
when the cylinder is turned to the locked position, I can't get the key
out.
Not with either lock cylinder.

Is there a trick to this, or do I just need more patience and fiddling?

( my hunch at the moment- parts that are slightly worn, now nice and clean
and not quite fitting right)

Any suggestions welcome

thanks all

Bill M
82 GL I4