Are you SURE the oil leaking isn't the valve cover gaskets? Oil leaking from the head gaskets on an M117 doesn't ring a bell for me.

If you have the manifold off, replace the rubber seals, they are cheap. Ditto for injector seals, although they are not a problem

I'd only do valves if you have some evidence they are in need of repair -- normal time to valve job with decent maintenance is 200,000 miles on these engines.

However, if the cams show signs of wear, I'd do a complete valve job now rather than piddle around and end up taking the heads off two or three times.

You have hydraulic tappets and will have to check them the book way. I have mechanical tappets, so can't help you much there.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!