I use a die grinder with a wire brush attachment to clean off the remnants of the old gasket after first using a razor blade. The razor blade is in a holder that converts it to a scraper.

I don't use any gasket cement or sealer on the gasket. I do however use silicone on the Oring on the heater pipe as well as the opening it slides into on the pump. It acts as a bit of lube as well as an extra measure of sealing.

I make sure the mating surface for the seal on the head is very clean and I even put a thin layer of silicone there as well as on the seal.

I consider the design of the contact between the head and the water pump to be a very poor one. I count on my water pumps lasting 100,000 miles. However, in my experience that seal will need to be replaced at least once or perhaps twice before 100,000 miles mark is reached. I find the seal that comes with the Hepu pumps to be a better quality than the ones available aftermarket.

Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal