This URL might help with replacement of the monovalve insert:
Be sure that you get the small silvery-looking plate on top(4 screws) snugged down good; otherwise, you'll lose coolant.
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.