only the rear main seal, but a good time to check ur clutch, if it's on it's way out, do it at the same time.
and the timing will be easier while the engine is out too. may as well do ur tappet cover and cam seals at the same time too, well atleast ur cam seals. the rear main is the dearest seal and the rest of them, cam x 2 and crank cost about the same as the rear main when added together .