I'm going to replace the rear main and the balance shaft seals while the engine and gearbox are separated. The Haynes manual details pressing the new main seal in until it is flush with the outer edge of the seal housing in the block. However the original seal is pressed in beyond that to a recessed depth of ~ 4.2 mm from the edge of the housing. I would think it is best to place the wiping edge of the new seal in the same spot on the crankshaft as the old one? Or should I follow instructions and install it to flush with the housing edge?
On the 1200 rear main seals that I have installed (only a few) they were originally pressed in below flush. I never measured the depth as I used the (special) flanged BMW seal driver & bushing to install the new seals. That special BMW driver drives the seal to well below flush (that 4.2mm would be a good guess, but as I mentioned, I never measured it).
I can't remember if there is an oil drain back hole in front of that main seal but if there is then make darn sure your new seal doesn't block any oil holes.
The only time I would mess with a seal depth change is if there is a worn ring on the crankshaft, if you do change the seal depth, then as mentioned above, make sure that you are not blocking an oil drain-back hole or that the seal will contact a spinning flywheel bolted to rear of crankshaft.