Failed B2 Piston install

I replaced the B2 Piston with the transmission in the car. Also replaced the sleeve and seal.

I did a three mile test drive and all seemed well, no leaks. I thought we were ready to start driving it again. I went to put fuel in and drove 2 miles and lost all the fluid. Got it towed back home and looked at the B2 cover. It was partly hanging out of the transmission. The snap ring was partly
still in place. I have a parts car with a good transmission that I want to install. I am wondering what could have caused this failure. I removed valve body so I could make sure the dog leg was where it should be.I thought the ring in place all the way around. I know the groove was clean where the ring goes..I suppose there couldn't enough pressure on the piston to do this.

What is the purpose of the tab with hole?


Any comments will be apprieciated

Thanks, Tom

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