Is it something that I should to with the engine out? Or if it aint broke dont fix it?

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

If you are going to remove the upper oil pan, then you should replace at least the half that is on the pan. If you are going to replace the main and rod bearings, then it is a good time to do the other half of the seal under the crank. I would peek to see if it is leaking back there to determine if it is needed.

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1983 123.133 California
- GreaseCar Veg System

It would be very hard to do the top half with the engine in the car. Until recently, I thought it would be possible to replace the bottom half with the engine in the car but somebody posted that they couldn't get the upper oil pan off with the engine in place so perhaps it is not possible to replace the bottom half with the engine in the car either.
I wouldn't even consider doing it unless it was absolutely essential or the engine had to come out for other reasons.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Replacing the seal didn't take but a minute. I also did bearings, oil filter housing gasket, and opened the oil pump to check the bushings. It has too be on the stand as other have said.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"