If it's a thick piece of felt, it's a holdover from the 4 cylinder days in the late 1920's when the rocker arms got lubed by squirting oi through some small holes in the valve cover with a hand-pump oil can to saturate the pad. Later 216's and newer engines didn't have that pad, so it probably won't hurt to remove it. A better idea would be to find where the valve cover is warped and straighten it. Remove the cover and invert it on a workbench and use something like a long carpenter's level and a feeler gauge to check for bowed spots that are failing to put pressure on the gasket. Repeatedly overtightening the valve cover hold down nuts can warp the valve cover and upset the sealing surface.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!