I'm considering rewiring my tt. the question is whether i should go for a three prong powercord or keep all the grounding duties on the phono lead or should i split grounding duties between the power cord and phono lead?

I believe given the high impedance and low output of cartridges, I would use a dedicated ground wire and stick with a two prong plug. Depending on the type of motor in the TT, you might want to use a non-polorized plug, so you can reverse it. Sometimes if hum is an issue, this can reduce it the hum level.

Do not touch the power cord. If you are having hum look for the problem somewhere else.

The output of a cart is soooo small that even the tinest of ground loops will hum enough to make the unit unlistenable.

Stick with a two-wire config.;)