When trying to do an offline windows repair I kept getting error 0x800f081f, source files could not be found. Here are two things to fix this.
1. Identify the wim index you want to use. You can get the index details with the following command:
dism /get-imageinfo /imagefile:x:\sources\install.wim
2. Now use the following command to run the repair. X is the drive letter of your image and the number 2 can be changed to be the index you identified in step 1. Adding LimitAccess restricts this command from reaching out to windows update:
dism /online /cleanup-image /restorehealth /source:WIM:X:\sources\install.wim:2 /LimitAccess
3. Once the scan is successful run the last command to complete the repair:
sfc /scannow
Error: 0x800f081f