It's not a sealant, rather a small rubber O-ring.
If you look at the blown up diagram of that job you'll see the small O-ring they refer to.
If you go to your local MB dealer they should have one, or you can try Lowe's or Home Depot -- it's a standard size ring that fits snugly over the 13mm bolt, as that bolt goes thru the timing cover and into the chamber.
Good Luck
