The hook up of oil systems consists of substantially two components - cooler lines and oil filter housing.

The oil filter housing should have been swapped when you had the engine out of the car where it is easy to work on. Note: When you get the oil filter housing off an SD make sure you get the SDs cooler lines as well as they are very different. You might also want to get the turbo line, although this is not nearly as critical (I didn't get it). Also get any brackets and other hardware as they are different and it may come in handy in making up a support bracket. (The R4 compressor was removed because of clearance issues, and the R4 bracket provides support for the oil cooler lines.) 

You can use the stock oil cooler, lines and fittings if you desire. I elected to use aircraft fittings and stainless steel braided oil lines on mine. The major reason was that I read the horror stories about replacing lines and decided that I wanted to replace lines easily instead.

How to Use AN-style oil lines

In order to use AN style fittings you need to modify the oil cooler to accept -10AN fittings and also braze on -10AN fittings on the oil cooler hard lines.

First cut off the threaded portion of the oil cooler fitting.

 

Then drill it to 3.4" using a step drill. DO NOT attempt to drill using a standard drill as it will catch and ruin your cooler, guaranteed.

 

Then tap it 1/2NPT

 

Clean out the ends of the cooler completely using a solvent to remove all the shavings. If you don't get everything it is likely not fatal, as the cooler is upstream of the filter. I elected to use 90 degree fittings although you could also use other fittings, including the stock MB fittings with -10AN fittings brazed on just like for the cooler lines.

 

Here is a shot of the bracket I fabricated to support the cooler hard lines. You can see the AN fittings on the lines just for fitting. I didn't trust gas welding/brazing skills, so I had them done at an A/C shop very reasonably. 

 

And here's the final product installed on the car (from the bottom looking up)

 

If these lines ever leak, they can be removed and new lines installed reusing the same fittings. The beauty of AN fittings is that they are designed and intended to be reused.

Remember to hook up the turbo supply line. If you kept the 300D one, you'll need to tweak it just a bit around the back of the engine. Be sure to use new gaskets to prevent leaks. It would also be a good time to replace the o-rings on the dipstick tube, and the oil return tube from the turbo.

You will also want to either cap the return line on the oil pan from the oil separator (300D doesn't have one), or hook up your own oil separator to keep cleaner air going to the turbo inlet.

There is one more oil related issue to be aware of, and that is the oil pressure gauge. We'll cover that in the gauge section, but you can either use the mechanical gauge from the 300D or the electrical gauge from the 380SL, which means you'll either connect the oil pressure line to the oil filter housing or screw in the electronic sender off of the 380SL