I'm an owner of a few 123 bodies and looking at an SD. I"m wondering if there is any substantial increase in parts costs on the SD vs the 300d turbo 123's.

No.

The W123 is the more common vehicle so the parts will be a bit less costly. But, in general, the pricing for parts and repairs on the W126 from '81 to '85 is reasonably close to the cost of the W123.

I agree, very little difference and I've owned both my 123 CD and my wife's 126 SD since new.

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Houston, Texas
1984 300CD 235K miles, Elvira, one owner
1987 300TD 180K miles
1974 TR6 78K miles Sarah Jane, one owner
OBK #27

Of course you think it's cheap, ... you have a pre-Bosch Disco!!

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Gone to the dark side

- Jeff

A lot of the parts on a W126 are the same as those on a W123.....so they would be the same.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

How if at all, does the 300 SD engine differ from the 300D turbo?

The throttle linkage is slightly different.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

The oil pressure sender is electric instead of a tube.