This is a DIY.
Now this is how I did it on a 123. I think your 190 is similar.
Disconnect the neg cable to the battery. safety first
Remove the instrument cluster, will make it easier to reach in to work.
place key in position 1 or 2, think 2 and insert a paper clip into the hole in the tumbler.
Reach in and remove the plug at the rear of the assembly. this is the ignition switch.
Unscrew the collar and remove the tumbler.
Remove the little black plug
Remove the 2 vac lines to the shut off valve. be sure to mark them so you know what side they go on.
Remove the 10mm bolt that holds the clamp on, may have to access it from under the dash.
Slide the clamp to the side to expose the button. see the picture I posted above. it is the brass colored button. I think it sort of faces to the front of the dash. push it in, rotate the lock assy. this will keep the button in the tube depressed. I had it pop back in the hole 3 times before I got it out.
Wiggle the assembly to the right away from the steering column and pull out.
It`s a little tight quarters, but it will come out.
Looking All Parts Express, looks like the 190 parts has to be ordered seperately. when I ordered the one for my 123, it came with a new ign. switch and the vacuum shut off valve.
So you will have to R&R the parts off your old one to the new one.
2 screws for the vac valve, and 3 for the ign. switch.
slide in the new assembly into the tube.the little button will pop back in the hole. tighten down the clamp. plug in the little black plug. plug in ign switch plug. Install the 2 vac lines to shut off valve. Install the tumbler and collar.
Replace the instrument cluster.
think that is about it.
Charlie
Your tumbler might be ok, but if you shot it with WD-40, might be a good idea to wash it out with some soap and water, and blow it out with air.