Precisely what years and what models are affected by the wiring harness problem? Is it only cars built from 1992 to 1995?

Also, if the plastic sheathing on the harness in back of the engine is falling apart and disintegrating, should the plastic sheathing be replaced? If so, can I buy an inexpensive sheathing that is slit along its entire length to use as a replacement sheathing (instead of the expensive sheathing from MB which is not slit, and probably therefore difficult to install)?

Thanks very much for any help.

Mike