I can't push the key into the driver's side door lock on my 1975 200 series 2 door Volvo. The key slot is covered by a piece that usually retracts but it doesn't now.

1. Is there a way to fix the problem without replacing the lock?

2. If I have to replace the lock, do you know where I can buy one?

3. Is it possible for someone with some basic mechanical skills (me) to replace the lock if need be?

Thanks in advance!!