Gear oil thrown around rear diff

I have a 76 GMC Burb C25 2WD w/a 454 engine and the TH400 behind it. I believe it has a full floating rear axle and 3.73 gears based on the RPO codes.

I had a shop completely service the rear axle earlier this year (new seals, brakes, bearings, service diff, etc). A few weeks ago, I noticed a small leak on the floor underneath the rear diff area. I look under and everything looks fine on the rear facing side of the diff -- dry and nothing out of place. On the forward facing side of the diff however, where it connects to the driveshaft -- it's quite wet. In addition, the floor pans above + the shocks on both sides + the section of the dual exhaust pipes that face the diff are also all wet with what looks like gear oil (translucent green fluid). The driveline itself, however, is completely dry. I checked the diff fluid and it was full enough to still drip gear oil from the fill plug. The vent tube for the rear diff seemed to be in place correctly and with the check vent valve in place at the end.

I cleaned up the area with some brake clean and rags. I left it overnight and didn't see any seeps or leaks. I took it out for a drive and sure enough the same scenario showed up again as if gear oil is getting sprayed around the forward facing side of the diff in all directions.

Any ideas on what it could be?

Pinion seal. Only thing you can do is make sure the vent is clear and not plugged. Otherwise you need a pinion seal. The yoke probably has a groove in it, which if you just got a pinion seal, is probably why it's leaking.

Pinion seal and possibly yoke.