Regarding Comfrey, it is hard to extract the root into oil.
I have not used mullein flower oil for years as I usually use either Calendula or Saint John's Wort oil for anything I would use Mullein oil for. They are both easier to make as far as I am concerned. SJW has to be made with a heated oil extraction too.
My favorite salve is plain Calendula. It does everything I want a healing salve to do and it is easy to extract into oil.
I use to make more complicated salves when younger, but I have simplified things in my old age. It was really fun experimenting when younger and I use to like to make complicated mixtures. Now I am more practical.
Hugo Morvan wrote: Tendinitis it helped with