I am in no position to give advice on what oil to use or how long to leave it in the engine between services. You will have to decide on your own, but all oils will absorb contaminants form both air and combustion gasses, hence the oil will go bad over time even if the engine has not been used between oil change intervals.<br><br>Re: filters; I have studied these extensively an have determined by testing them, info in consumer reports, and actually cutting them open, I have been able to determine the best quality and construction for my Bronco & money. From a standpoint of being able to filter out particles that are truly harmful to engine components. And being engineed to go at least 6,000 miles. Let me just mention 3 brands. Motorcraft, Wix/Napa (Wix Builds filters for NAPA), and, AC Delco. All the other most popular brands that were tested were acceptable for approx. 4,000 miles but on the average, if you happen to go past that by a couple thousand miles, some would get plugged elements and begin to bypass. The next time you have a few extra bucks and some time, If you are not using one of the 3 brands mentioned, go and buy your brand and one of three above, cut the canister all the way around the circumference of the seam with a hacksaw. This can be done by threading the filter onto a piece of pipe clamped in a vice. Open both filters and compare quality and construction of the internal components. it should be obvious to you which filter, at the very least has better designed construction.