I had a similar leak on a 722.315 transmission(83 300TD) about a year after I had it rebuilt, not related to any recent service on it, but after a 3000 mile drive across the plains at interstate speeds. Looking up into the "grate " on the bottom of the transmission, I could see drops of ATF on the bolt heads of the bolts that hold the front cover on the transmission. The rebuilder sent me a new radial seal and gasket for the front cover which I installed but still had the leak. There was no evidence that the radial seal was leaking--it was dry.
So I had to pull the transmission a second time( I am getting good at it) and when I removed the front cover again, there was ATF in 4 of the 9 bolt holes through the cover. Since the threaded bores for these bolts are blind, the only way fluid can get in the bores of the cover is if the gasket inner edge is not making a seal with the cover/transmission housing adjacent the bores. The lowest bolt in particular has only a 2.5mm wide section of gasket material to make the seal due a material cutaway behind the cover. Once the fluid is in the bores of the cover, there is only a spring or wave washer under the bolt head to seal it, against a non-machined surface of the cover. The torque on these bolts is only 13 Nm.
The rebuilder was very helpful and sent me a new(rebuilt) torque converter(just in case it was the problem) and I again replaced the front cover gasket, but also bought some Parker Stat-O-Seals (Google it), which are washers with a molded rubber seal on the inside diameter that is deformed as the bolt is tightened. These replaced the spring washers. This time I was successful and have no leaks. It is hard to understand why this leak showed up after a year from the rebuild, but it did. In your case, one would suspect that it is related to the recent service- an overfull transmission might exacerbate the problem.
Let us know if removing some of the fluid stops the leak.
Peter