I am on my second Dyna and have always changed my own oils and filter at regular intervals (depending on driving conditions and mileage). I also take my bike in for the schedule maintenance at the dealership (where they replace all fluids per mileage schedule). I would like to start doing more myself and had a question (possibly a dumb one) about the trany fluid. My manual calls out the drain plug for the oil is located on the side of the pan, and the transmission plug is on the bottom. Now, forgive a few stupid questions. • Doesn't this mean both the engine and trany are sharing the same oil? • If so, does it matter on the type of synthetic oil I use? • Also, if they are shared, since the trany plug is lower, when I drain my oil, isn’t some of the 'old' oil still in the case??