Finch, sorry the housing gasket didn't solve the leak. Next step is to look at the seal assy and the inside of the pump housing - sorry, I completely ignored the fact that the housing itself could be cracked . You obviously know how to get the housing apart and back together as you changed the housing gasket. This time take a look at the inside of the housing for any obvious cracks in the body (it's unlikely, but possible that the body failed) - if you find no cracks, it's time for the SP 1600 Z 2 (my bad- there is another part that has the "C" before the "Z 2") This thread covers a lot of what you'll need to do - the difference is that you'll use the 7/16" wrench to 'lock' the shaft while unscrewing the impeller. Once the impeller is off the seal plate will 'fall off' the mounting plate. Inside the seal plate is a ceramic and rubber seal - to get it out, turn it face down and put a flat head screwdriver on the back edge and 'knock it out'. The part on the impeller you want to take a good look at so you'll be able to put the new one on correctly - know which end goes towards the impeller and which goes against the ceramic piece! I always lube the rubber on the seal plate piece and also the impeller piece - it doesn't hurt and things go together a little nicer (... more nicely?) Screw the impeller back on, using the 7/16 wrench to hold the shaft - hand tight should be enough, but 1/8 turn extra with a wrench won't hurt (DO NOT GO 'CAVEMAN' on the impeller!!) Reassemble the pump as you did when changing the housing gasket (the housing gasket should still be good - as long as the visible part of it isn't flattened to the housing - & yes non petrolium grease will only help it). I think I've covered it all - however, there is thisthread wherein Tenax gives his experience and warnings.

If you need any clarification on this - please ask
p.s. Please !! be sure to have the power off to the pump when working on it... but you know that