The following comes from a book written by W. Robert Nitske, titled "Mercedes-Benz Production Models Book 1946-1995".
According to the book, the 300SE-300SEL equipped with M103 motor was made from 1985-1991. I believe the car was available in the U. S. from 1988-1991.
There's no individual timing listed for each year. The book provides the following:
Acceleration - 9.6 sec - 0-100km/hr.
This timing is for the 2962cc M103 motor.
Your friend's '88 300SE is equipped with such an engine.
I own a 91 300-SEL and feel the car has all of the power I'll ever need. If you're a high performance nut and used to driving power cars, the 300SE/300SEL may not exactly knock your socks off.