My suggestion is, it you ran an OS plug in the head button, use OS plugs for that button. If you want to use a GRP/Ninja plug, get a button for that glowplug. I have seen them leak, not just this brand, but all others when you switch up glowplug brands. I have heard people tried the OS plug and went back to the GRP glowplugs and said they didn't feel as good as the OS, but this could be because the taper is now not sealing properly.

I have been hearing the GRP is closer to the Picco taper than any other plug, but I would still say stick to GRP plugs unless you are certain you have no leakage issues with another brand.