Home-made sealed freewheel?
As far as the increase in drag after a few weeks, I reckon the Chain-L oil is to blame for that. As far as oils go, it's not all that heavy, and over a few weeks can migrate out from where it needs to be inside the freewheel.

One of my favorite things to do with an old free wheel is to soak it in degreaser/solvent/parts washer overnight. Then, use rags and compressed air (or opening it up, if you like tiny bearings in abundance) and clean out the degreaser. Once the freewheel is bone dry, slowly dribble in some Phil's Tenacious Oil while spinning it. Ill often set the freewheel onto a freewheel tool in a vice and spin it with one hand while holding the Phil's bottle in the other.

The dry freewheel will ratchet very loudly, but you'll hear it quiet down as the very thick oil begins to penetrate. Once you start to see some oil come out the other side you know you're done.