I'm not going to mess with this at all! Looks like honest dust, maybe some mud dauber action. No leads. Case is cracked. Handle good. Of course, you are going to need to go through this. It will look great in on your bench as you test classic gear....

Here's the good news! Appropriate assembly and instruction manual included. Yeah... 

Vintage Heathkit Multimeter MM1 Untested Project. Condition is "For parts or not working". Shipped with USPS Priority Mail.