In all fairness to Tektronix,the terminations I have had occasion to see "torn down"were of uncertain age.
Normally,they are very reliable,so you may find terminations in the average workshop which date back to the age of
the 545B,with matching characteristics.
If you aren't a Tek part No. guru,they all look pretty much alike.
The ones I've seen look as if they were hand made,where leaded resistors would be the easiest type to use.
Maybe the newer ones use SMD components.
It is fun to check terminations with a Spectrum Analyser,Tracking Generator,& a Directional coupler.
Out of one 50 ohm term that looked like the OPs one,another with a fluted grey plastic body,several 50 ohm 1kW
Test Loads,& two 20dB attenuators in cascade,the latter gave the best result (80dB return loss),with the big Test
Loads next,& the two so-called 50 ohm terminations the worst.
No, I don't have the figures to hand,it was done several years ago at work.
I'm not sure if the Attenuators were Agilent or Bird,the Test Loads were Bird and a generic Chinese one,the terminations were generic also,possibly from RS Components.
From memory,the tests were over about a 300MHz range,centred on 480 MHz.
VK6ZGO