Hi Todd - If your engine is like my 90, the drain plug is on the driver's side of oil pan and has a crush ring. If you buy a filter from Roger Tyson at 928sRUs, he usually tapes a new crush ring to the box. I'd have to look up the torque specs on the bolt, but it's not very much - make sure it's snug but DO NOT overtighten. Here are the filling capacities and engine oil specs from the 1986 US mode owners manual. I'm not sure how warm it gets in the Ohio summer, but 15W-50 is probably fine, as is 20W-50. Mobil 1 synthetic is very popular, as are oils from Redline, Torco, Brad Penn. The most critical thing other than viscosity is the oil MUST have sufficient zinc anti-wear (ZDDP) in the amounts of 1200ppm or greater. Our engines do NOT tolerate modern low viscosity oils with lesser ZDDP amounts. Hope this helps!
Jarrod Wise
90GT
928 Owners Club President
928 Registry Chair