Try rescue tape.(the stuff for fixing holes in radiator hose ) It will seal much better than teflon tape, and hold up to fuel exaust fumes and high temperature much better. You will only need one layer or so. Teflon tape is not meant for fuel/oil high temp. applications. this stuff IS. Personally though I use red RTV.
I have heard of putting an x-tra crush ring in to move the seating surface of the o-rings out slightly, so they are no longer in the grooves. But this may adversley effect perfomance by moving the pipe out from the head ever so slightly. Not sure, but if you could get them to seat in a different location that would get them to seal better. I would also condition ALL of my o-rings with dielectric grease(silicone jelly, R/C Car diff lube) prior to using them.
With a grooved exaust port even brand new o-rings will not seat properly without some sort of assistance. The only real way to solve the problem is have the walls of the port filled up with material (weld) and machined back to spec. ($$$)