88-91 300-SELs use a Bosch H9DC or H9DC0 plug. Std. setting is .032; however, there are some on this list who believe a better idle is attainable using a slightly wider gap. I haven't experimented with widening the gap yet.
The H9DC0 plugs have a slightly wider side electrode and in my opinion, last a little longer than H9DCs.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.