Is the bearing loose to the point where it slips in and out by hand or with very little effort? If it is, then it is probably leaking past the outside of the bearing. The bearing will move side-to-side and up and down enough to let the oil leak past.

It could be the O-Rings as Bob suggested they could be cut or hard. You should notice that quickly upon inspection.

The internal coupler system is good about not leaking if the seal is good, the o-rings are good and the bearing fits tight in the bore. Avoid using silicone unless you have to in a last minute fix. As far as a spring in the yoke goes, you don't have to use one to keep it from leaking unless you are using the driveshaft to hold the lower shaft and coupler/bearing in place. That is the wrong application for that as the spring should only be used to control the float of the shaft and not actually hold a great deal of pressure on the lower shaft/driveline itself.
The torque tube has a recess built into it to clear the bearing, but it also helps keep it from moving forward, but has enough clearance to allow it to "walk" a little in the bore.

If the bearing is loose, we have built sleeves similar to the ones in the sprint car rears to tighten the bearing up in the bore. Staking or siliconing the bearing in place is a temp. fix at best and usually just a futile waste of time.

Often on a Winters midget rear;the flange bolt holes(on the face) will break through when they are drilled and tapped(usually in the 11 o'clock or the 1 o'clock position) and leak. It is possible that it is leaking past the flange and into the tube, but usually it covers the outside of the rear. That is fixed with a set screw with dope or silicone in the bore.

email me if you wish leadersedge@earthlink.net

Good Luck,

Scott Baue