My textbook (Physiology 9th edition, People's Medical Publishing House, Beijing) tells me that coagulation factor V is produced in endothelial cells and platelets, which is different from some other books (saying in liver). So where exactly is it produced? Or is it just not quite clear?
Factor V is indeed mainly produced in liver (Wikipedia), which releases it into blood plasma.
But platelets are also an important source of factor V and "may account for "~25% of the circulating factor V" (ref 1)
The following reference gives a much more detailed explanation of factor V
Reference (available as free pdf)
Factor V Is Complexed with Multimerin in Resting Platelet Lysates and Colocalizes with Multimerin in Platelet α-Granules * Catherine P.M. Hayward Emilia Furmaniak-Kazmierczak Anne-Marie Cieutat Michael E. Nesheim John G. Kelton ** Graham Côté
The coagulation factor 5 is primarly produced in the liver, meaning that the liver isn't the only place where this factor can be produced (F5 can possibly be produced by megakaryocytes too). After it is manufactured it circulates in an inactive form and is then converted into the active form with the help of thrombin and is able to attach to platelets. However, as far as I know, factor v is not produced in endothelial cells, there are a few factors that are, like Von Willebrand factor (VWF), factor VIII, thrombomodulin, endothelin etc., but F5 is not one of them.