This gives you the general idea (although on a 126): http://business.baylor.edu/Richard_Easley//autofaqs/b2piston.htm

On a 123, some have done it with the trans in the car by dropping the rear support and, I believe, loosening the exhaust and manhandling it.

There was a recent post on the B2 in a 123, changed out with the tranny still in the car. Check the "search" with in the field and good luck.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)