I don't know how marine grease reacts in suspension oil but I have heard that you shouldn't use White Lithium grease on suspension forks. It apparently gets gummy in suspension oil and can clog up damping ports. If you aren't sure you should probably go with a safe bet and buy some suspension specific grease like Slick Honey. The o-rings on suspension forks are fairly resistant to petroleum products so marine grease probably won't ruin the o-rings.