Hey there! I haven't used any gasket sealant where the 2 gaskets meet and in my case it woudln't help as the leak wasn't coming from where the 2 gaskets met, the leak was coming out of the gasket on the straight stretches. Some additional silicon rubber gasket on install may help there, but I'm not sure, only time will tell.

In terms of the piece I was referring to, it's similar to what's seen in this threads first picture:
https://5series.net/forums/e60-discu...et-n62-149915/

I've read those should be removed when installing back the valve cover.