white = unburnt fuel (usually the case since our cars run rich until the manifold heats to operating temps. this is when the o2 sensor starts reading and adjusting air/fuel mixture)
Its easy to do the valve seals. You can even do it without pulling the head if you set each piston to TDC so the valve doesnt fall. However the issue is why are the seals leaking and the answer is the valve guides are probably worn on a 93 with high mileage.