Here is the specification for the oil seal situated on the distal finish of the bean can on my /79 R80. This seal had hardened and shrunk over time and was leaking crankcase oil previous the shaft into the bean can – not good to have your ignition floating in oil! This seal shouldn’t be accessible from BMW.
It is form of an odd measurement – not frequent however nonetheless accessible: 12.5mm id, 20mm od, 5mm thick. It is accessible from Harwal.com for $3.70 cents plus a $5.00 minimal cost order. There’s a pressed in place washer that you’re going to must take away to tug the previous seal. The seal is situated beneath this washer. This washer is pretty tender so watch out eradicating it so to not bend it. I changed the seal and washer with appropriately sized sockets and mild faucets from a hammer.
It is clearly a good suggestion to switch the massive rubber O ring on the base of the can on the similar time – that is accessible from a minimum of one Vendor and presumably BMW as nicely. I sourced mine on the ironmongery shop.
Maybe it will assist somebody considering a rebuild… maintain ’em hummin. 
