Do engine builders actually dip the entire piston in
oil and then stick them in the cylinder?
The best way to make sure that the rings seal (my experience of course) is to make sure that the cylinders are super clean and of course has the correct finish for the rings used. I have always used ATF. After final wash, get all the residue with thinner, I place ATF on a lint free white cloth and saturate it with ATF and wipe out the cylinders and make sure it comes out clean. If not clean again. Leaving a film of ATF in the cylinders. Wipe a small amount around the rings and a spot on each skirt and install. Seals every time.