I have a 1988 rx7 TII. Just redid the waterpump, runs great, but there seems to be a coolant leak coming from somewhere, but dripping right in back of the oil pan. The weird thing is the coolant only leaks when the RPM's are above 3k.

 

Coolant leaks- especially little ones- can be a real PITA to track down because the spot it drips from can be so far from where it actually started (does that make sense?).

If it's leaking from the driver's side rear of the oil pan the first place to look is the heater hose line from firewall to rear iron.

You can always get the car up to operating temp, shut her off and then listen for hissing as the coolant heatsoaks/expands and maybe track it that way.