The thicker one-piece gasket material has changed significantly from a few years ago.
The one I got in 2006 was grey and has lasted on my daily 235 ever since without any leaks.
However the one I got for my 261 last year from the same place (Larrowe's) was now white in color but lasted for only a few miles before it developed cracks and leaks around EVERY exhaust port...
Ask for the grey material, if any are left and avoid the new white ones.
I ended up with the standard manifold gaskets set from an original GM NOS 261 gasket kit and it has held up nicely for about 3000 miles now without any leaks.
These original gaskets have a black coating on the metal side and are a little thicker than the new shiney ones available today.
