I also have a Saturn ('99) SL1 and have been following the saturnfans.com website, lots of good advice there. Their feeling is do not use high mileage oil, it causes the rear main seal to swell too much and fail. For sure, check the oil every time you fill up. Also use a fixed orifice PCV valve, it will reduce your oil usage. Part numbers available on the website, also check for leaks, method on the website, and use copper core spark plugs, NGK, P/N on website. Mine was a rolling wreck when I got it right after my van got totaled by a deer, but now I get up to 40 mpg. and it is reliable and fun to drive. Also check the website for the oversized oil filter numbers, I've been using a Wix. As for oil, I would go with a decent 5W-30 synthetic, I'm using Mag1 and am happy so far. 5W-30 is what the owners manual suggests.