My brother is selling his 1991 Buick Park Avenue with 115K and in pretty good shape, he already picked up a late 90's model Blazer with 234K on the clock. I drove it tonight and it seems to ride and drive well. I figured with 234K miles a 10w40 could prove beneficial as if I remember correctly these like to develop bottom end issues. Its the 4.3 V6. Is 10w40 taking it too far? He said at hot idle the oil pressure gauge on the dash reads 18-19ish, whether or not that is accurate I don't know. May I add, he is not the easiest on his cars.