In article ,
RonLee wrote:

My tach cable housing (Lycoming) leaks nasty black stuff so I cleaned
and dried it. What is the best lubricant to use? Particularly one that
does not deteriorate and leak through the housing. What about a
covering for the housing to prevent the leaking?

The best way to deal with this is to replace your mechanical tachometer
with an electronic one from EI.