I'm medium/thick and texlaxed, but castor oil weighs down my hair as well. I don't use it anymore, but when I used to use it, I found that using it as a prepoo worked better than as a sealer.
JBCO is also heavier that CO, so maybe using the clearer one might be better.
Diluting castor oil with another lighter oil works well to if you wish to use it on dry hair as it will still provide the thickness qualities of the oil you are seeking as well as not weighing the hair down.
Last, another way it worked for me was by mixing it in deep conditioner. I would separate the amount I was using and add castor oil to it.
Using castor oil on dry hair was a no no for me, but on wet hair, it went really well.
Please excuse my iPhone; it's trying to get it together