These old engines were built in the days of "normal" diesel. As such, the engineers relied on the high lubricity of the diesel fuel to lubricate the injector pump. Fast forward to today when we've outlived the low-sulfur fuel era and are now saddled with ULSD (ultra-low sulfur diesel) with comparatively no lubricity.
Do yourself a favor and add 1-2% two stroke oil to your fuel to restore lubricity and protect what's left of your IP
- cheap insurance!