Llyn:
The lub. Tee handle is Accucraft's invention (figuratively maybe not literally - I've not seen or experienced every loco in the whole wide world). I only know a few Accucraft loco models that have plastic covered metal lub. caps, like K-28s. And it is not old versus new loco's issue as the new C-19's have Tee lub. caps:
The Tee cap can be a PITA not just a pain to the fingers, either from being really hot or digging into your fingers trying to loosen it as it "expands" when hot.
Yours is a good practical tool and very similar to what a lot of us have done for the Tee cap. We take the Accucraft water pump handle and cut slots up the sides in line with the flat slot for Accucraft's water pump's shaft. Then the pump handle slips over the Tee and you twist. So the pump handle does double duty, pump handle and Tee handle. Like your tool both make removing or installing the Tee cap a lot faster.
Or the best solution for a Tee cap, cut the horiz. bar off and put a wheel on the vertical shaft, like a plastic spoke wheel handle (used to be available from Coles).