1997 Chevy Cavalier leaking water outlet

Heater problem
1997 Chevy Cavalier Two Wheel Drive Automatic 54000 miles

Hi. I have a 1997 Chevy Cavalier Z24, 2.4 Litre engine with 54000 miles. I replaced a broken water outlet a few months back. I had the water pump replaced last week and now the water outlet is leaking. It seems to be leaking at the mating surfaces.
The outlet an odd part, made of plastic and instead of having the usual paper gasket, it just has a tube on the back that goes about an inch into the coolant cavity with a rubber o ring as the only gasket specified for the outlet. The bolt holes have metal sleeve inserts, so you can only tighten so much. It doesn't seem to leak when running, only after it's set for for a few hours, it's a very slow leak. No overheating. There seems to be no information available online and even the service manual gives no specifics.
I'm considering making a paper gasket, using sealant on both surfaces, and either using teflon plumming tape or some kind of thread sealant in case coolant might be coming thru the bolt holes. If you have any suggestions, I'd love to hear them.