thermostat housing leak

I had the same leak on my LD340 when I bought my Dart last year. When I took it apart over the winter I assumed it was because of the old thermostat housing so I bought a new chrome one too. Likely the same one you have.
I'm just in the process of reassembling the engine and now I'm wondering if I'll still have the same problem that you're having.
I like you're o ring idea. I just might look into doing that now while it's still apart.

Ted