1979 450SL

my Key started sticking a couple of weeks ago and i ordered a new one and it did not help. the keys work in every other lock but the ignition.

any advise on quick fixes? is it mechanical or is there any electrical that could be wrong? the steering wheel will lock in place?

help i have been stuck for some 15 min before it worked and need to fix it?

are there instructins anywhere on how to replace if that is what i need to do?