Brace the shaft on a block of wood, then drive off the front housing by hammering down on the mounting ears.
Be careful the shaft doesn't pull out of the barrel and rotating assembly. If this happens, all the pistons will pop out and it will be a pain in the butt to get it all back together.
Note the thrust bearing and thrust races.
The two o-rings on the barrel housing are the ones that were leaking on this compressor.
Clean the o-ring grooves very thoroughly and carefully. Place barrel and rotating assembly in a clean place. Do not allow it to get dirty or it will be irreparably damaged.
Now, remove the snap ring, shaft seal, and o-ring.