Rebuilt Thermoquad issue -- It has to be primed before start each time

If only the oilpans are full, then your test will only prove the oilpans. I was suggesting you fill the entire float-bowl chamber. Oh nevermind I reread your post, and noticed the "and the bowls" this time
The oilpans themselves I would test with gas. This will give almost instant results.You'll see the JB turn color and change it's sheen, as it become moist.

Here's another test I just dreamed up; I have never done it. You should be able to invert the black body and submerge it in a pail of water, and if there is a crack, I wonder if the trapped air inside wouldn't find it and bubble out.