[Xavier]

I had the exact same thing happen to me with my motor, turned out to be the inlet water neck from the manifold. It would only do it when really hot, and it would drip, slowly like yours, so it would appear like it would come from every where else. There are a lot of comments on the Chrome water necks that are out there using substandard finishing or steel for the application. Once the water neck heats up (or even not heated) the base becomes (or is) slightly dished where mounted to the manifold. Once cools, it seals tight, once hot, it slightly becomes unsealed. Most of these beautiful water necks, are Chinese, and have this issue.

I swapped mine out for a two-piece Stainless Steel billet water neck (entirely overkill, but a work of art) and never had the problem again. I since then replaced it with a FE style surge tank, so if you want it, make me an offer. It is absolutely solid, and is worth every penny. It is a shame something so nice is just sitting on my work bench.