the spiral groove is about 3/16' wide, with a rounded bottom like it was machined with a ball mill. If it has crud in it, the crud will block the flow back up the spiral into the tcase, and the pressure may force lube past the seal. You can pull the dust protector to get a better look - hard to see past the splined output shaft. Is the yoke still non-rocking on the splines? Still tight? Did the spring come out of the seal as it was driven? I always pack the spring groove with axle grease before I drive it to keep the spring in, and lube the sealing surface with either silicone lube or axle grease.