In taking apart the steering head on my '93 K75 standard to replace the bearings, there's some sort of seal between the upper and lower bearings, with two retaining screws that hold it in place (You can sort of see what I'm talking about at 16:47, here).

When I look at realOEM for my bike's serial number, it doesn't show up in the parts fiche at all. IT doesn't even show the retaining screws that stick through the steering column to keep the seal in place.

Does anyone know what I'm talking about? What's the BMW part number for this mysterious seal that I can't find in any parts diagram?

It's the Fluid Bloc steering damper.

roach374 wrote:When I look at realOEM for my bike's serial number, it doesn't show up in the parts fiche at all. IT doesn't even show the retaining screws that stick through the steering column to keep the seal in place.

What's the BMW part number for this mysterious seal that I can't find in any parts diagram?

Use only the last seven digits of your moto's serial number. You also needed to look in this section.

Regardless, here is the realOEM page you couldn't find. Scroll down for the part numbers.

Point-Seven-five wrote:It's the Fluid Bloc steering damper.  

What he said.  

From memory it was introduced around 1991 and is generally a pain in the rear end.  The grease inside them dries out and makes it a pain when trying to set up steering head bearings.

The special grease is still available as Dow Corning High Vacuum Silicone Grease.
Regards Martin.

Laitch wrote:Regardless, here is the realOEM page you couldn't find. Scroll down for the part numbers.

As usual, Laitch, coming through in the clutch. Thank you!

MartinW wrote:The special grease is still available as Dow Corning High Vacuum Silicone Grease

Thanks MartinW, What's so "special" about this grease? Could I use red grease, SuperLube, or white lithium or something instead?

The grease is extremely thick, and the Fluid Bloc is designed to use that particular grease. A tube of that grease will last you and your ancestors for many generations to come. I've found other uses for it. It can be packed between the upper dust seal and the fork seal to stop the ingress of dirt and water. I've never had to change my seals in over 20 years, replace the grease every year or two. I also use it under the boot of my rear master cylinder to stop water and road crap ingress. A lot of master cylinders I've seen have corrosion around and under the boot. 
Regards Martin.