impalabuilder.... start another post and ask when the MB M119 engines began using plastic oiler tubes. I'm thinking the date was post 95 - but this is a guess.
I've never tried looking in the oil fill cap for the tubes. Sounds like a good idea. Here is a link to someone changing the oil filler tubes.. at least it will give you an idea of what you are looking for.
http://www.baxnet.com/merc/oilguides/story.htm different car but same engine.
Has your you upper wiring harness been replaced? If not, as mentioned before, moving the hardened hoses, upper wiring harness, and plug wires might cause additional problems. If you decide to tackel the job, make sure you order replacement valve cover gaskets before disassembling the valve covers. Insure the mating surface of the valve cover and engine is fee of all oil and torque the cover bolts to only 9nm. The gasket goes on dry. Pay special attention to the rear area of the gasket during assembly.