Genuine DeWalt Gasket — part number 391315-00. This flat sealing gasket fits between the gear-case and cover to restore a reliable dust/oil seal and stop weeping or debris ingress — made from a durable composite rubber material and sold individually.

Direct-fit examples: DW716 and DW718 mitre saws (listed in those parts diagrams), and the DWS780 of 12" sliding compound mitre saws. Other compatible models include : DWS779, DWS782 and DHS790T2 / DW716 / DW718 — verify the model and type number from the side of the saw to confirm fit.

Simple swap: remove the gear-case cover, lift out the old gasket, seat the 391315-00 gasket in the original groove and reassemble—restores the original seal and keeps the gear case protected.