Just added 2nd bottle of RX after running 2000 miles on regular oil. Plan on running this dose for 1000 miles. My question is should I change the oil filter for the last 1000 miles or just keep the one that's on there now. And, can you even change the filter without draining the oil. This is for a 95 Toyota 22RE. Also, I plan on putting around 3-4 oz from now on in future oil changes for maintenence. Is this correct? Thanks for your help!!! Rando