I have been using a synthetic automotive CV joint grease made by Redline for the last 6 years that works very well. Seems to have the same 'stickiness' and viscosity as the grease that came with my Robart, JetLegend, Skymaster struts over the years. Same translucent red color, same sticky and hard to clean up texture.

The Redline stuff is kinda hard to find (generally used in performance and racing applications) but I'd think most synthetic CV grease would be similar. Don't try the cheap "moly" CV grease, it is not 'sticky' enough and tends to run easily (and is a nasty gunmetal grey color that makes your struts look dirty)....

Barry