this is getting interesting!
anyhow, as soon will remove it for painting, will know what it is in my case.
i worked for many years at factories where sometimes things were changed and there were no notices.
so, perhaps we find ourselves in a situation similar. as i said, soon will know and tell. and as the primer that i will use is recommended for metal and fiberglass, i hope it will do.
we'll see.
thanks anyway you all for this advice.