I like your procedure for replacing seacock backing plates - quick, uncomplicated, and effective.
IDUNA is fitted with W-C seacocks and except for the two seacocks under the sinks, all seacocks are fitted with two brass grease cups from Essex Brass -
] Figure 85.
The grease cups provide a means to grease the seacocks in the water. I open the seacock, pressurize the grease in the cup by turning the T-handle on the greaser, then wiggle the seacock handle using a slight back and forth motion. I employed a similar procedure when I greased glass petcocks in the lab.
I did not fit greasers to the seacocks under the sink to save space. When I want to grease these, I screw zerk grease fittings in the two 1/8' NPT drain holes in the seacock body and use a grease gun. Sometimes, I loosen the two nuts on the seacock plug before pumping in the grease.
For a grease, I use Shell Retinex LC2 for seacocks, winches and engine. This grease is formulated with lithium salts and a "tackifier" for marine applications. Based on my conversation with a Shell engineer, the "tackifier" is added to all marine greases to improve the resistance to water washout. Retinex LC2 is sold as a truck grease with no reference to marine applications. My experience using Retinex LC2 is it works better than Spartan seacock grease.