A very small amount of proprietary sealant is used, not enough that you would see much when you take them apart. Aftermarket sealant has been identified elsewhere on the discussion group!
Precision machining is a wonderful thing! No gaskets!
I'd replace the rails, chain, and oil pump while you have the engine out! Why wait for something to break? IP timing will return to factory setting when you change the chain when you pull it through, too!
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!