Door lock problem
 

Car - 1986 300E
Problem: The lock cylinder cover plate for the driver's door has gone missing. I don't know if it just fell out or if someone made an attempt to open the car. The lock still works fine but I had to cover it with tape to keep the rain out. I've been using the locks on the other door or the trunk to get into the car.

I looked at the problem in AllData and they said the entire cylinder has to be replaced, the cover is not available separately. Also they said that, in 1987, the cylinder cover was swaged on instead of peening it on. Maybe the original design was poor.

My questions:
1. Is there any point in looking for a salvaged lock to either swap the cylinder cover or to have it keyed to my old key?

2. If I look for a new cylinder, keyed to my present key, I assume I'll have to go to the dealer. Has anyone done this? About what do they charge? ( I looked at the instructions for removing the lock cylinder and I think I can do that part of the job.)

Thanks for your help.