Slixtiesix,

If you store stock developer in airtight bottles (500ml pop bottles will do) filled to the brim it will last longer than 7 months. As you empty the bottles, squeeze out as much air as possible. IIRC, Perceptol uses metol, not hydroquinone, and won't oxidise like an MQ dev. I could be incorrect though.

Cheers,
kevs