Ran out of my 5 minute edit limit.
Added,,
Drilling into the tumbler & not interfering with the housing, will allow you to install a replacement complete tumbler with key.
You have to have the main key in the tumbler to collapse the little keys, & the whole assy should slide right in
You then turn the key probably 90 deg. to remove the key, & lock the assy. in place.
I would also make sure you have the housing cleaned out really good first, & then lube the new assy. with like 3 &1 oil , Rem oil works fantastic also .