The below info is for the real Bosch New Style Hand Primer. Febi and some other make compies so there is no telling what is inside of them. I have also read that there is counterfit Bosch Parts in the Market Place.
Bosch Hand Primer has Dual edge Viton® seal:
HandPrimers
New style hand primer used with bio diesel
New Style Hand Primers use with Bio Diesel - PeachParts Mercedes ShopForum