Is this a repairable item or does the entire distributor have to be replaced?

If you are talking about the o-ring that seals the distributor atop the airflow sensor (sitting in a groove surrounding the plunger), I have replaced these on other makes so I would imagine yours can be too. It's pretty simple to do. Depending on access constraints it can probably be done w/o undoing the fuel lines. It was so long ago now that I can't remeber the specific symptoms that led me to replace it. I do remember that the results were quite dramatic though.

I thinhk we're talking about the same thing. The o ring around the plunger connected to the airflow plate that adjusts the fuel delivery to the injectors. It's located in the center underneath the fuel distributor. The dist has to be removed and opened up to access it.