Posted to the diesel discussion, because mine is a diesel, but realize I should probably have posted here first as the central locking is likely common to both gas and diesels:

Hope it's okay to link to that posting, but hoping E320 or similar owners may have some info regarding their experiences of replacing keys on older cars:

Can copy and paste if that's better? Questions are in the post below:

'96 E300D Replacement key/fob

Thanks, and please let me know if this kind of cross-post is forbidden or there is a better way of doing this.