Mercedes: ignition lock, switch lock, lock cylinder

Question
My father has a 82 Mercedes 300SD. Yesterday he put the key in ignition and it would not turn. Completely locked up so car had to be towed home. Is this a common problem, can he replace the ignition switch, lock housing, tumbler?  

Answer
These threads should have the answers you need.

How not to remove the ignition lock! Butchery at its finest.
http://www.mercedesshop.com/shopforum/showthread.php?t=148451

Fixed my lock cylinder on driver's side
http://www.mercedesshop.com/shopforum/showthread.php?p=1056089&posted=1#post1056...

Ignition Cylinder Tumbler replacement; mixed diesel/gas
http://www.mercedesshop.com/shopforum/showthread.php?p=1065596#post1065596

Ignition Cylinder, Switch, or Housing?
http://www.mercedesshop.com/shopforum/showthread.php?t=145832