Why I add 12% (one gallon) of gear lube at every oil change...

[dumptruckisx]

Is Gear oil recommended for a CM2350? Im purchasing a used truck and looking to read up on everything i can but im curious if the previous owner used synthetic oil instead of conventional then i cannot use gear oil as i will have to continue using synthetic oil. Am i on the right track is this correct? please correct me if im wrong. Im going to have to do an oil analysis as i have no way of knowing if its synthetic or conventional in there and if its already synthetic then i wont be able to switch to conventional and add gear oil in anyway. Im new to this kind of thing so sorry if its a dumb questions i just couldnt find the answer anywhere so looking for your guys professional opinion on this type of situation for a used truck purchase that may already have synthetic oil what should a buyer do?