I have a leak at the 2 copper washer/ seals at the top the fuel filter mounted on my Perkins 4108. I have remove these washers and clean them up as best as I can including  a light sanding with find sandpaper. I’m still getting a constant slow seeping leak. I’m hesitant to crank down too much on the bolt as I realize this filter fitting is made soft metal and I don’t want to share the thread.

Are these washers intended to be crush sealing washers? I’m about to go get some replacement copper washers but it’s not clear to me if these should be replaced regularly when one changes out the filters and if they are basic copper washers or’s crush sealing washers. 

Any output on this small but critical matter is much appreciated.