Its a big can with one or more pistons (depending on your vac model). The piston seals are not the hard part.. the slave cylinder seals and the vac diaphragm are the more 'unique' parts.
Biggest issue with 'vac cans is water pitting the bottom of the cylinder. I can be repaired, but usually its better to move up to a Series Three or Four 'vac for parts availability.
