The link treetops shows is for the 95-97 N/A engine and then has another view for the 98-99 turbo style.

The 98-99 turbo breather is a single connection at the rear of the valve cover, (#35) that goes through a puck (#30) bolted roughly over top of cylinder #5, then goes forward (#65 and 68) and angles out (#71) at an exit point across from cylinder 1 injector. This goes into the intake tract (#74) just ahead of the turbo inlet.

The 95-97 breather outlet goes to the plumbers nightmare where it is shot into the intake manifold at all 12 points above the intake valves.

The engine inlet side of the breather is the same for both engine types.

I suspect the part that fell in would be #35, that is the only part that penetrates the valve cover on a 98-99 engine.

Also for the OP: if you pull the valve cover you will need one #17 and six #23, these are the seals around the injector wells. These can leak and if they do, the injector wells will fill up with lube oil.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech