[sailingdog]

You generally do not grease delrin nylon bearings. They're not designed to be used with grease, and if you grease them, they will generally gum up with dirt and dust and wear much faster. They're supposed to be rinsed occasionally, but not greased at all.

 

[sailingdog]

The grease fittings might have been used to provide additional lubrication and to help exclude water from the rudder fitting, which would reduce the risk of the stainless steel corroding.

However, if the previous owner didn't use the zerk fittings to fill the area with grease on a regular basis, it would probably be worse for the stainless steel, since it would not displace the water and trap it against the stainless, leading to increased corrosion of the stainless steel.

Without a better view of the top of the rudder stock, where the stainless steel piece is, which does appear to be fairly corroded, it is hard to say what caused the problem. The band of corrosion does appear to line up with the channel in the delrin though.

 

[sailingdog]

Delrin is probably lower maintenance than roller bearings. The problem with using a graphite composite is that graphite can cause serious galvanic issues with aluminum, since it is more noble than the aluminum.