I just resealed my steering box last weekend and it was actually easier than expected. The gear box is marked by a small notch on the steering shaft spline. I don't know if you just replaced yours with a rebuilt one, but if so, go look at the old box and check for the marking so you have an idea of where it is.

*Update*
I added a photo so you have an idea. The Pitman arm is also marked. You have to look on the steering shaft on the smooth part and you will see a thin marking line. If you get the box lined up to center as if you were getting ready to mount it in the vehicle the line would be at the area facing forward towards the front of the car.

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1990 190E 3.0L