Suburban Water Heater help

I have what appears to be an older version of the SW6DE. When I got the trailer the anode rod was out of its hole and laying there. My issue to even see if the heater works is the threads for the anode rod are rusted and covered with buildup. I have been working on cleaning them but I am wondering if that part is replaceable. The threads on the rod are also rusty so ordering a new one but not sure if I can get it screwed in. It is going to be difficult with the condition of the threads in the hole.

I don't even know how the rod was even in the hole because the buildup was so much that you couldn't see most of the threads. I think perhaps the buildup underneath is due to excessive thread tape.