Best Gasket Maker / Sealant for Air Cooler Cap

[PamlicoTraveler]

I have a Yanmar 4jh-hte (turbo). Had to remove my air cooler assembly cap to track down a missing vane from the impellor. When I reassembled and put the cap back I used a gasket maker to seal it. When I put the cap back on the air cooler it was leaking heavily (water flooding through the seal.)

I ordered the Yanmar gasket and it still leaked. So I am trying to figure out what else I can do to seal the connection between the air cooler cap and the air cooler. I need something that would seal it. As I mentioned, I first tried some heat tolerant gasket maker, but it wasn't filling the gap for some reason ; not hard enough. Conceptually it seems like something like butyl tape would he thick enough to completely seal it, but I don't think it would be suitable for an engine seal, and particularly where hot water flows.it needs to be heat tolerant, but also thick.

Do any of you engine gurus have an idea what would work? Some iknd of rubber- like seal?