External Slave Cylinder troubleshooting

[War_Pony89]

In uncharted territory, removed slave to fix something else. Pressure inside the unit blew the piston out the end. Problem is I don't know what should be there on the to hold the spring tension where it is covered by the boot. Looks to me there should be something, but I can't find any parts or schematics on this thing. It's from Advance Adapters, and I guess I need to buy a new unit? Hoping someone has some experience to provide some guidance if it can be fixed?