That is a high wattage resistor. It is about 2 to 2.5 inches long so I will guess in the 25 to 50 watt range. The value/part number is probably on the back side or bottom. You'll have to drill out the rivet to verify.
That resistor is probably $10 to $15 dollars.
Now for the opinion....
I can't speak for newer Magnetek converters, but I have worked on several old Magnetek converters, 2004 and older, and I would not fix it. The output was not filtered and controlled like todays converters.
I suggest replacing with a modern Progressive Dynamics multi-stage or another brand of equivalent output. They are microprocessor controlled and have multi-stage charging which is much better on the battery.
Look on line, I picked up one about 2 years ago for $60. Currently I'm seeing 100 - 150 on ebay.
Good luck.