Scott, I wonder if the resistor may have been replaced with one from a contaminated load or a water load,
not knowing the history on it makes it a Sherlock Holmes case.?
Measuring near 50 Ohms dc does show it has a good resistive element though.?
There are two types of elements used for load resistors like this, one is a glass rod with the film deposited on it, the second is made of bulk carbon.
I've seen the first type have a contaminated film on the surface over the carbon that causes it to show increasing RL vs freq.
This occurs in water loads used for long periods with tap water.? Calcium or magnesium or something in the water binds to the surface of the resistor and affects the performance vs freq.? I knew first hand this happening with a person using well water to cool a Bird load.
Not sure if old oil can contaminate a load though.?
The remedy is to clean the resistor rod using alcohol followed by baking soda in hot water.??
?If that fails then a new resistor might be available from Altronic Research in Yellville AR. They make resistors.
GL? Reid? W6MTF
Brandon DX