Water Pump O ring

Just finishing up an engine rebuild on my 91 3Cyl. I've tried 3 or 4 O rings on the out put tube of the water pump and it still leaks a bit. I was hoping to avoid using a sealant but will if I have to. Does anyone know of a source for better fitting O rings, or if I need to use a sealant what do you suggest? Thanks for any help.

Dave

When mine leaked on my '93 I got a replacement ring at the GM dealership parts department for a few bucks. Normally I avoid getting parts there, but in this case it was cheap and the correct size. They had it in stock and with a little grease on it, it stopped the leak behind the water pump.

Thanks GeoJim, that makes the most sense.

Dave