My trunk lock will not turn

I own a 1982 300TD. I locked my trunk the other day with my key. I then tried to unlock it today with my key, but the lock will not turn.
Does anyone have any suggestions why my lock will not turn with the key. I don't think its a vacuum issue because the vacuum for the trunk has been disabled for years. Can anyone help me?
God bless,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.