Just bought an '89 Honda Prelude 4W Si and trying to figure out what weight oil to use. I believe it called for 10W-30 in engine and manual tranny. But now people use the Honda MTF in transmission. Just wondering if I should stay with 10W-30 or go to 5W-30. Looks like owner has been using Castrol 5W-30??? It has 172,000 miles and is in "perfect" shape....