Some of the best gear I used for years the guy used castor oil with 1% low BB and another solvent ...advantage was zero pain and superior levels of hormone easily in the oil 3-400 mg per ml. Was taking pops every 3 days so it really didn't matter on half-life.
Only thing was when I switched to sub-q it would leave lumps and hard to inject....new guy uses GSO....
Tons of articles out there back in the day on using thicker oils to slow down absorption and release of shorter esters like tren ace back before there was tren enanthate .