The tank under the seat is for 2-stroke injector-oil. Down near the kickstart is the transmission/clutch oil. It takes 1100cc of 10-30 motor oil in my ´78 DT250 and is more than likely the same with your bike. However I prefer to use 10-40 oil in my transmission because of the high temperatures it is subjected to with limited airflow. Change your transmssion oil every 1000 miles and before storage by removing the larger drainplug on the bottom of the crankcase (where a 4-stroke engine oil plug would normally be) and refilling with the proper lubricant for your bike. There is no filter. TIP: Do not overtighten the plug! Doesn´t need to be super tight. If it leaks then the plug gasket is bad and tightening will only strip your plug or worse your crankcase threads.