Marco,

Have a look at this link: http://www.retrophotographic.com/moerschchem.htm

The Moersch SE2 Warm developer keeps for a number of weeks in its diluted working strength form.

So not all WS diluted developers are 'one-shot', use only once then throw away. Clearly there are some out there that keep well (if in full containers) and can be reused.

Regards,
Trevor.