Pharmacy castor is usually very expensive atleast it is here and not needed for our model engines.
All you need is first pressing castor oil without any additives, maybe second pressing also is good enough. Not so hard to tell the quality, just look in the oil buttle and if it is clean yellowish or colorless then it is good. I use a first pressing castor oil that comes from India but maybe castor oil is also locally made in your country? I mix this castor oil with Aerosave synthetic oil in 50/50 ratio. There is no need to run any engine dry or using after run oil, simply not needed and not worth the extra hassle.

Marcol,
I dont understand what is wrong with a castor/syntetic blend? Many very well known glow engine manufacturer still recommend a castor/syntetic blend to be used.