sm465 broken snap ring

[76stepsidechevy]

Anyone good with these? Drove home 40 mins on the highway last night fine and then stopped at the off ramp, first was fine second worked but sounded like the trans was full of marbles and 3rd was fine. I dumped the oil this morning and pulled a side cover, found a snap ring in 3 pieces in the bottom of the case. Ive got the top cover off now but can't for the life of me find where this snap ring came from. I'm guessing it holds second gear in place on the shaft and it's jumping around making all the noise.