Well, I could probably do it at home, but I've done it before. It's possible to do it at home I guess you could say, no factory tools involved or anything like that. It's mainly removing the under-dash panel, reoving the connector, then squeezing in these 2 plastic pins that releases the electrical switch from the lock housing. Probably a little bit harder than my description.
Easier, I'd say, then replacing one on a 201 or a 124, for example.
The underdash panel is a little difficult to remove on a 140 chassis.
DON'T assume this is what the problem is without diagnosing it. I AM NOT saying this is what your problem "has" to be!