Hello, I just noticed a small leak from the Thermostat housing (graphite). I want to replace it with a metal housing. Please share your experience, pro & cons. I'm having it done. Thank in advance.
My lady 2005 Jaguar XK8, 80K. I have a photo, will upload later after I figure out how to.

There is no aluminum alternative for the 4.2. I replaced mine due to a leak a couple of years ago.

I see you have posted on another thermostat thread. That thread is about the 4.0 thermostat, not the 4.2 that you have. The crack in the seam is not unusual.