You don't need to ask questions, Woodford are correct ones and good people you can trust.
I use MATT LEWIS 01922 692424, ace service, and around the 75 pound mark same ones genuine INA which are GERMAN.
You do not need to worry about suitability as Matt only sells the correct ones.
I use SILKOLENE PRO S, as do others and it is a fantastic oil, pricey but you get what you pay for!!
tabetha