a-904. Still leaking after rebuild! :(

There is a possibility of knocking the spring off the inside of the pump seal also, just so you know to watch for it.
The spring will ride around the converter snout until the converter comes out again, then it can drop into the pump.
I used to put a little assembly lube in the back of the seal before it went in to keep the spring in place while the seal got tapped in.

The seal can also pop out after it'a all back in the car also, and they have a spring steel retainer for that if needed. (red locktite on the seal always worked for me)

But if it doesn't leak anymore it was probably just overfilled, or foamed and overflowed on startup as already mentioned.